LIBRARY 


UNIVERSITY  OF  CALIFORNIA. 


Class 


CLAYS 


THEIR    OCCURRENCE,    PROPERTIES,    AND    USES 

WITH   ESPECIAL   REFERENCE  TO   THOSE   OF 
THE   UNITED   STATES 


BY 

HEIKKICH   BIES,    PH.D. 

Professor  of  Economic  Geology  in  Cornell  University ;  Fellow  Geological  Society  of  America  ; 

Member  American  Ceramic  Society  ;  Member  American  Institute  of  Mining  Engineers  ; 

Author  of  "Economic  Geology  of  the  United  States  " 


FIRST    EDITION 
FIRST   THOUSAND 


NEW  YORK 
JOHN  WILEY   &   SONS 

CHAPMAN   &   HALL,    LIMITED 
1906 


Copyright,  1906 

BY 
HEINRICH    RIES 


ROBtET  DROMMOND,   PRINTER,   NEW  YORK 


PREFACE 


FEW  mineral  products  have,  perhaps,  been  more  extensively  treated 
in  the  scientific  and  technical  literature  than  clay,  but  the  published 
facts  are  widely  scattered,  and  many  of  them  are  not  always  easily 
accessible. 

It  has  therefore  seemed  to  the  author  that  there  is  a  demand  for  a 
comprehensive  work  on  the  subject,  which  may  be  of  value  to  geologists, 
chemists,  and  others  interested  in  clay  and  its  applications. 

As  the  title  of  the  work  indicates,  the  subject  is  treated  mainly  from 
the  American  standpoint,  and  in  the  preparation  of  it  the  author  has 
drawn  freely  on  his  own  published  reports  as  well  as  those  of  others. 

The  arrangement  of  the  subject-matter  of  the  State  descriptions  by 
geologic  formations  has  been  selected  as  permitting  the  greatest  uni- 
formity of  treatment,  and  those  desiring  to  look  up  the  distribution  of 
any  one  kind  of  clay  can  easily  do  so  by  reference  to  the  Index. 

Credit  for  information  is  usually  given  in  foot-notes;  but  where  some 
particular  report  has  been  freely  drawn  upon,  this  is  indicated  by  a 
parenthesis  containing  the  number  of  the  reference  in  the  bibliography 
following  each  State. 

The  author  wishes  to  express  his  thanks  to  Dr.  G.  P.  Merrill  of  the 
United  States  National  Museum  for  many  helpful  suggestions  received 
during  the  course  of  his  work;  and  to  Mr.  S.  Geijsbeek  of  Seattle,  Wash., 
for  assistance  rendered  during  the  compilation  of  the  manuscript. 

Acknowledgments  are  similarly  due  to  Professors  C.  S.  Prosser  and 
E.  Orton,  Jr.,  of  Ohio  State  University;  Prof.  H.  A.  Wheeler  and  Mr. 
Lemon  Parker  of  St.  Louis,  Mo. ;  Prof.  I.  A.  Williams,  Iowa  Geological 
Survey;  Dr.  E.  A.  Smith,  Alabama  Geological  Survey;  Dr.  G.  P.  Grims- 
ley,  West  Virginia  Geological  Survey;  Dr.  W.  B.  Clark,  Maryland  Geo- 
logical Survey;  Dr.  D.  H.  Newland,  New  York  Geological  Survey;  Dr. 

iii 


155021 


iv  PREFACE 

H.  B.  Kummel,  New  Jersey  Geological  Survey;  and  Mr.  H.  Leigh  ton, 
Cornell  University.  Dr.  W.  B.  Phillips,  former  State  Geologist  of  Texas, 
has  kindly  given  the  author  permission  to  publish  the  facts  relating  to 
that  State. 

For  the  loan  of  cuts  the  writer  is  indebted  to  the  American  Clay 
Machinery  Co.,  Bucyrus,  Ohio;  Chambers  Brothers  Co.,  Philadelphia, 
Pa.;  Henry  Martin  Machine  Co.,  Lancaster,  Pa.;  and  Bergstrom  &  Bass, 
Brooklyn,  N.  Y.  Many  others  have  kindly  loaned  photographs,  and  to 
each  of  these  acknowledgment  is  made  under  the  respective  illustrations. 

CORNELL  UNIVERSITY,  ITHACA,  N.  Y., 
July,  1906. 


CONTENTS 


PAGE 

PREFACE iii 

CONTENTS v 

LIST  OF  ILLUSTRATIONS xi 

LIST  OF  ABBREVIATIONS xvi 

INDEX - .  469 


CHAPTER  I 

ORIGIN  OF  CLAY. '. 1 

Definition,  1;  Weathering  processes  involved,  1;  Kaolinization,  3;  Kaoliniza- 
tion  by  pneumatolysis,  5;  Residual  clay,  7;  Kaolin,  8;  Form  of  residual  deposits, 
11;  Distribution  of  residual  clays,  12;  Transported  clays,  14;  Sedimentary  clays, 
14;  Origin,  14;  Structural  irregularities  in  sedimentary  clays,  17;  Classification 
of  sedimentary  clays,  18;  Marine  clays,  19;  Estuarine  clays,  19;  Swamp  and  lake 
clays,  20;  Flood-plain  and  terrace  clays,  20;  Drift  or  bowlder  clays,  20;  /Eolian 
clays,  23;  Classification  of  clay -deposits,  23;  Orton's  classification,  23;  Wheeler's 
classification,  24;  Ladd's  classification,  24;  Buckley's  classification,  25;  E.  Orton, 
Jr.'s,  classification,  26;  Grimsley  and  Grout's  classification,  26;  Ries'  classification, 
27;  Secondary  changes  in  clay-deposits,  28;  Mechanical  changes,  28;  Tilting, 
folding,  faulting,  28;  Erosion,  30;  Chemical  changes,  33;  Change  of  color,  33; 
Leaching,  35;  Softening,  35;  Consolidation,  35;  Concretions,  35;  Formation  of 
shale,  36. 

CHAPTER  II 

CHEMICAL  PROPERTIES  OF  CLAY 40 

Minerals  in  clay,  40;  Hydrous  aluminum  silicates,  42;  Kaolinite,  42;  Minerals 
related  to  kaolinite,  48;  Halloysite,  48;  Indianaite,  50;  Pholerite,  50;  Nacrite, 
51;  Rectorite,  51;  Newtonite,  51;  Allophane,  51;  Le  Chatelier's  experiments, 
51;  Quartz,  52;  Feldspar,  53;  Mica,  53;  Iron  ores,  54;  Limonite,  54;  Hematite, 
54;  Magnetite,  55;  Siderite,  55;  Pyrite,  55;  Calcite,  55;  Gypsum,  56;  Rutile, 
56;  Ilmenite,  56;  Glauconite,  57;  Dolomite  and  magnesite,  57;  Hornblende  and 
garnet,  57;  Vanadates,  57;  Tourmaline,  57;  Manganese  oxides,  58;  Vivianite, 


Vi  CONTENTS 

PAGE 

57;  Rare  elements,  58;  The  chemical  analysis  of  clays,  58;  The  ultimate  analysis, 
58;  Interpretation  of  ultimate  analysis.  59;  Variation  in  chemical  composition  of 
clays,  60;  Variations  in  the  same  deposit,  60;  Rational  analysis,  61;  Comparison 
of  ultimate  and  rational  analyses,  62;  Method  of  making  ultimate  analysis,  64; 
Method  of  making  rational  analysis,  66;  Mineral  compounds  in  clay  and  their 
chemical  effects,  68;  Silica,  68;  Hydrous  silica,  70;  Iron  oxide,  71;  Sources  of 
iron  oxide  in  clays,  71;  Effects  of  iron  compounds,  72;  Coloring  action  of  iron  in 
unburned  clay,  72;  Coloring  action  of  iron  oxide  on  burned  clay,  72;  Fluxing 
action  of  iron  oxide,  75;  Effect  of  iron  oxide  on  absorptive  power  and  shrinkage 
of  clay,  76;  Lime,  76;  Effect  of  lime  carbonate  in  clay,  76;  Effect  of  lime-bearing 
silicates,  78;  Effect  of  gypsum,  78;  Magnesia,  80;  Alkalies,  82;  Titanium,  84; 
Effect  of  titanium,  85;  Water  in  clay,  86;  Mechanically  combined  water,  86; 
Chemically  combined  water,  87;  Carbonaceous  matter,  88;  Effects  of  carbon  in 
clay,  88;  Effect  of  water  on  black  coring,  90;  Soluble  salts,  90;  Origin,  90;  Quan- 
tity of  soluble  salts  in  a  clay,  92;  Prevention  of  soluble  salts,  92;  Method  of  use,  92. 

CHAPTER  III 

PHYSICAL  PROPERTIES  OF  CLAY 94 

Introductory,  94;  Plasticity,  94;  Definition,  94;  Cause  of  plasticity  in  clay, 
96;  Water-of-hydration  theory,  96;  Texture  theory,  96;  Plate  theory,  97;  Inter- 
locking-grain  theory,  98;  Ball  theory,  99;  Colloid  theory,  99;  Molecular- attraction 
theories,  103;  Effect  of  bacteria,  104;  Weathering  clay,  104;  The  measurement 
of  plasticity,  105;  Tests  of  the  wet  clay,  105;  Tests  of  the  dry  clay,  108;  Texture, 
108;  Definition,  108;  Mechanical  analysis,  108;  Methods  of  separation,  110; 
Beaker  method,  110;  Schoene  method,  113;  Hilgard's  elutriator,  114;  Centrifugal 
separator,  115;  Relation  between  composition  and  texture,  117;  Tensile  strength, 
120;  Definition,  120;  Practical  bearing,  120;  Relation  to  plasticity,  120;  Meas- 
urement of  tensile  strength,  120;  Cause  of  tensile  strength,  123;  Shrinkage,  128; 
Air-shrinkage,  128;  Fire-shrinkage,  129;  Measurement  of  shrinkage,  132;  Poros- 
ity, 134;  Specific  gravity,  136;  Determination  of  specific  gravity,  137;  Fusibility, 
137;  Incipient  vitrification,  138;  Complete  vitrification,  138;  Viscosity,  138; 
Effect  of  chemical  composition  on  fusibility,  139;  Homogeneity,  144;  Influence 
of  texture,  144;  Condition  of  oxidation,  145;  Expression  of  fusibility,  145; 
Bischof's  formula,  145;  Seger's  formula,  146;  Wheeler's  formula,  146;  Methods 
of  measuring  fusibility,  147;  Direct  methods,  147;  Seger  cones,  148;  Thermo- 
electric pyrometer,  153;  Wedgewood  pyrometer,  154;  Lunette  optical  pyrometer, 
154;  Classification  of  clays  based  on  fusibility,  154;  Indirect  methods,  155; 
Changes  taking  place  in  burning,  156;  Dehydration  period,  157;  Oxidation 
period,  158;  Vitrification  period,  159;  Effects  due  to  variation  in  the  clay, 
159;  Loss  of  volatile  products  in  burning,  161;  Color,  161;  Color  of  unburned 
clay,  161;  Color  of  burned  clay,  161;  Slaking,  162;  Permeability,  163;  Absorp- 
tion, 163. 

CHAPTER  IV 

KINDS  OP  CLAYS 165 

Kaolins,  165;  Chemical  composition,  167;  Physical  tests,  167;  Distribution, 
167;  Ball-clay,  168;  Chemical  composition,  169;  Physical  characters,  169;  Dis- 


CONTENTS  vii 

PAGE 

tribution,  169;  Fire-clays,  170;  Chemical  composition,  170;  Effect  of  silica,  170; 
Effect  of  titanium,  177;  Physical  properties,  177;  Analyses  of  fire-clays,  177; 
Occurrence  and  distribution,  177;  Uses,  179;  Stoneware-clays,  180;  Physical 
properties,  180;  Chemical  composition,  180;  Physical  tests,  181;  Terra-cotta 
clays,  182;  Sewer-pipe  clays,  183;  Brick-clays,  185;  Common  brick,  185;  Adobe,  . 
186;  Loess,  186;  Pressed  brick,  187;  Flashing,  189;  Enameled  brick,  191;  Paving- 
brick  clays,  191;  Fireproofing  and  hollow-brick  clays,  192;  Slip-clays,  193; 
Miscellaneous  kinds  of  clays,  195;  Clays  used  when  burned,  195;  Gumbo-clay, 
195;  Retort-clay,  196;  Pot-clay,  196;  Ware-clay,  196;  Pipe-clay,  196;  Sagger- 
clay,  196;  Wad-clay,  197;  Portland -cement  clay,  197;  Clays  used  in  unburned 
condition,  197;  Paper-clays,  197;  Mineral  paint,  198;  Ultramarine  manufacture, 
199;  Polishing  and  abrasive  materials,  199. 

METHODS  OF  MINING  AND  MANUFACTURE 199 

Methods  of  mining,  199;  Prospecting  for  clays,  199;  Outcrops,  199;  Springs, 
200;  Ponds,  200;  Vegetation,  200;  Exploitation  of  clay-deposits,  203;  Adapta- 
bility of  clay  for  working,  203;  Methods  of  winning  the  clay,  204;  Haulage,  209; 
Kaolin- mining,  209;  Underground  workings,  212;  Preparation  of  clay  for  market, 
213;  Washing,  213;  Details,  213;  Air  separation,  214;  The  manufacture  of  clay 
products,  217;  Uses  of  clay,  217;  Methods  of  manufacture,  217;  Building- brick 
and  paving-brick,  218;  Manufacture  of  brick,  218;  Preparation,  218;  Crushers, 
219;  Dry  pans,  219;  Disintegrators,  219;  Rolls,  219;  Soak-pits,  220;  Ring-pits, 
220;  Pug-mills,  220;  Wet  pans,  220;  Molding,  220;  Soft-mud  process,  220; 
Stiff -mud  process,  228;  Dry-press  and  semi -dry- press  process,  231;  Re-pressing, 
232;  Drying,  232;  Open  yards,  232;  Pallet  driers,  232;  Drying  tunnels,  232; 
Floor  driers,  236;  Burning,  236;  Kilns,  236;  Up-draft  kilns,  236;  Down-draft 
kilns,  239;  Continuous  kilns,  239;  Sewer-pipe  manufacture,  240;  Drain-tile,  247; 
Hollow  ware  for  structural  work,  247;  Manufacture,  251;  Conduits,  251;  Manu- 
facture, 251;  Fire-brick,  252;  Roofing-tile,  254;  Terra-cotta,  254;  Manufacture, 
254;  Floor- tile,  258;  Wall- tile,  261;  Pottery,  262;  Classification,  262;  Manufac- 
ture of  pottery,  263;  Preparation,  264;  Weathering  and  grinding,  264;  Washing, 
264;  Blunging  and  filter- pressing,  264;  Ball-mills,  265;  Tempering,  265;  Chaser- 
mills,  265;  Pug-mills  and  hand-wedging,  265;  Wedging- tables,  266;  Molding, 
266;  Turning,  266;  Jollying  or  jiggering,  266;  Pressing,  269;  Casting,  269;  Dry- 
ing, 270;  Subsequent  steps,  270;  Common  red  earthenware,  270;  Yellow  and 
Rockingham  ware,  270;  Stoneware,  270;  White  ware  and  porcelain,  271;  Elec- 
trical porcelain,  275;  Sanitary  ware,  275;  Bath-tubs  and  wash-tubs,  276. 


CHAPTER  V 

DISTRIBUTION  OF  CLAY  IN  THE  UNITED  STATES.     ALABAMA— LOUISIANA 277 

Introduction,  277;  Statistics  of  production,  277;  Alabama,  278;  Archaean  and 
Algonkian,  278;  Cambrian  and  Silurian,  281;  Lower  Carboniferous,  281;  Coal- 
measures,  281;  Cretaceous,  282;  Tertiary,  283;  Pleistocene,  283;  Division  of 
clays  by  kinds,  283;  China  clays,  283;  Fire-clays,  283;  Pottery-clays,  283;  Brick- 
clays,  283;  References  on  Alabama  clays,  285;  Arkansas,  285;  References  on 
Arkansas  clays,  286;  Arizona,  286;  California,  286;  References  on  California 


viii  CONTENTS 


clays,  289;  Colorado,  289;  Mesozoic,  290;  Pleistocene,  290;  References  on  Colo- 
rado clays,  290;  Connecticut,  293;  Residual  clays,  293;  Pleistocene,  295;  Refer- 
ences on  Connecticut  clays,  296;  Delaware,  296;  District  of  Columbia,  296; 
Florida,  297;  References  on  Florida  clays,  297;  Georgia,  298;  Palaeozoic  area,  298; 
Pre-Cambrian  belt,  298;  Coastal  plain  region,  301;  References  on  Georgia  clays, 
303;  Illinois,  303;  Ordovician,  304;  Coal-measures,  304;  Tertiary  clays,  304; 
Drift-clays,  304;  References  on  Illinois  clays,  307;  Indiana,  307;  Ordovician,  307; 
Silurian,  307;  Devonian,  307;  Mississippian  or  Lower  Carboniferous,  307;  Residual 
clays,  307;  Shales,  307;  Carboniferous,  309;  Kaolin  or  Indianaite,  309;  Coal- 
measure  clays  and  shales,  311;  Pleistocene  clays,  313;  References  on  Indiana 
clays,  313;  Indian  Territory,  315;  Iowa,  316;  Cambrian,  316;  Ordovician,  316; 
Galena- Trenton,  316;  Maquoketa  shale,  316;  Silurian,  316;  Devonian,  318; 
Carboniferous,  318;  Kinderhook,  318;  Augusta,  318;  Coal-measures,  321;  Cre- 
taceous, 321;  Pleistocene,  322;  References  on  Iowa  clays,  322;  Kansas,  326; 
Carboniferous,  326;  Triassic,  327;  Cretaceous,  327;  Pleistocene,  327;  References 
on  Kansas  clays,  327;  Kentucky,  328;  Ordovician- Devonian,  328;  Carboniferous, 
328;  Lower  Carboniferous,  328;  Coal-measures,  329;  Tertiary,  329;  Recent  clays, 
329;  References  on  Kentucky  clays,  330;  Louisiana,  331;  References  on  Louisiana 
clays,  332. 


CHAPTER  VI 

MAINE — NORTH  CAROLINA 333 

Maine,  New  Hampshire,  and  Vermont,  333;  References  on  Vermont  clays,  334; 
Maryland,  334;  Algonkian  clays,  334;  Silurian  shales,  335;  Devonian  shales,  335; 
Carboniferous  shales,  335;  Mauch  Chunk,  335;  Pottsville,  335;  Allegany,  336; 
Conemaugh,  336;  Cretaceous  and  Jura-Trias  clays,  336;  Patuxent,  336;  Arundel 
formation,  337;  Patapsco  formation,  337;  Rari tan  formation,  337;  Tertiary  clays, 
337;  Pleistocene,  337;  References  on  Maryland  clays,  339;  Massachusetts,  340; 
Residual  clays,  340;  Cretaceous  and  Tertiary  clays,  341;  Pleistocene  clays,  341; 
References  on  Massachusetts  clays,  342;  Michigan,  342;  Silurian,  342;  Hudson 
Rivrer,  342;  Devonian,  345;  Hamilton  shales,  345;  Marshall  series,  345;  Car- 
boniferous, 345;  Michigan  shales,  345;  Coldwater  shales,  346;  Pleistocene,  346; 
References  on  Michigan  clays,  347;  Minnesota,  348;  Residual  clays,  348;  Trans- 
ported clays,  348;  Pre-Cambrian,  348;  Ordovician,  348;  Cretaceous,  348;  Pleis- 
tocene, 351;  Loess-deposits,  351;  References  on  Minnesota  clays,  351;  Mississippi, 
352;  References  on  Mississippi  clays,  352;  Missouri,  352;  Palaeozoic  limestone 
clays,  354;  Kaolins,  354;  Flint-clays,  354;  Ball-clays,  355;  Stoneware  clays,  355; 
Coal-measures,  356;  Plastic  fire-clays,  356;  Stoneware-clays,  359;  Impure  shales, 
359;  Tertiary,  360;  Pleistocene,  360;  Loess  clays,  360;  Glacial  clays,  360;  Allu- 
vial clays,  360;  References  on  Missouri  clays,  360;  Nebraska.  362;  Carboniferous, 
362;  Cretaceous,  363;  Loess  and  alluvium,  363;  References  on  Nebraska  clays, 
364;  New  Jersey,  364;  Cambrian  and  Ordovician,  364;  Triassic,  364;  Cretaceous, 
366;  Lower  Cretaceous  clay  series,  366;  Clay -marl  series,  370;  Tertiary,  370; 
Pleistocene  clays,  371;  References  on  New  Jersey  clays,  373;  New  Mexico,  373; 
New  York,  375;  Residual  clays,  375;  Palaeozoic  shales,  375;  Hudson  River  shale, 
376;  Niagara  shale,  376;  Medina  shale,  376;  Clinton  shales,  376;  Salina  shale, 


CONTENTS  ix 

376;   Hamilton  shale,  376;   Portage  shale,  376;   Chemung  shale,  376-   Crete*    m/"" 
and  Tertiary  clays,  378;   Pleistocene  clays,  378;   References  on  New  York  clav 
382;   North  Carolina,  382;    Residual  clays,  385;   Sedimentary  clays  385-   Ref 
ences  on  North  Carolina  clays,  388. 


CHAPTER  VH 

NORTH  DAKOTA  TO  WYOMING 

North  Dakota,  389;    Cretaceous,  389;   Benton  and  Niobrara,  389;   Pierre  389- 
Fox  Hills,  389;   Laramie  and  Tertiary,  389;  Pleistocene,  390;  References  on  North 
Dakota  clays,  390;    Ohio,  390;    Ordovician  and  Silurian,  390;    Devonian,  392; 
Lower  Carboniferous,  392;  Coal  measures,  392;  Pottsville  formation,  393;  Sharon 
shales,  393;   Quakertown  clay  and  shale,  393;   Lower  Mercer  clay  and  shale,  394- 
Upper  Mercer  clay  and  shale,  394;  Mount  Savage  clay,  394;  Allegheny  or  Lower 
Coal-measures,  394;  Putnam  Hill  or  Brookville  clay,  394;   Ferriferous  or  Vanport 
limestone  and  clays,  395;    Lower  Kittanning  clay  and  shale,  395;  Middle  Kittan- 
ning  clay,  397;    Lower  Freeport  clay,  397;    Upper  Freeport  clay  and  shale,  397; 
Conemaugh  or  Lower  Barren  Measures,  398;  Monongahela  or  Upper  Productive 
Measures,  398;   Dunkard  or  Upper  Barren  Measures,  398;  Pleistocene,  398;  Refer- 
ences  on  Ohio  clays,  399;   Oklahoma  Territory,  400;   Pennsylvania,  401;   Residual 
clays,  401;    Silurian  and  Devonian  shales,  402;    Carboniferous,  402;    Pottsville, 
402;    Mercer  or  Alton  fire-clay,  402;    Sharon  upper  coal  fire-clay,  405;    Savage 
Mountain  fire-clay,  405;  Allegheny  or  Lower  Productive  Measures,  405;  Brookville 
clay,  405;   Clarion  clay,  406;   Ferriferous  coal  under-clay,  406;   Lower  Kittanning 
fire-clay,  406;   Middle  Kittanning  clay,  407;   Upper  Kittanning  clay,  407;  Lower 
Freeport  clay,  408;  Upper  Freeport  limestone  clay  or  Bolivar  fire-clay,  411;  Upper 
Freeport  clay,  411;  Conemaugh  formation  or  Lower  Barren  Measures,  411;  Monon- 
gahela group  or  Upper  Coal-measures,  413;   Pleistocene  clays,  413;  References  on 
Pennsylvania  clays,  414;    Rhode  Island,  415;   References  on  Rhode  Island  clays, 
415;    South  Carolina,  415,    Residual  clays,  415;    Coastal  plain  clays,  415;   South 
Dakota,  419;    References  on  South  Dakota  clays,  420;   Tennessee.  420,   Pre- Cam- 
brian clays,  421;    Palaeozoic  residual  clays,  421;    Carboniferous,  421;    Tertiary, 
422;    Alluvial  clays.  423;    References  on  Tennessee  clays,  424;    Texas,  424,    Car- 
boniferous clays,  426;   Cretaceous  clays,  426;  Lower  Cretaceous,  426;  Upper  Cre- 
taceous, 426;    Woodbine  formation,  427;    Eagle  Ford  formation,  427;    Taylor- 
Navarro  formation.  427;    Tertiary  clays,  428;    Lignitic,  428;    Marine  beds,  431; 
Pleistocene,  431;    References  on  Texas  clays,  433;     Utah,  434;    Virginia,  434; 
Residual  clays,  434;    Carboniferous,  437;    Triassic,  437;    Tertiary,  437;    Pleisto 
cene,  437;   References  on  Virginia  clays,  441;    Washington,  441;   Clay  shales,  441; 
Residual  clays,  441;    Glacial  clays,  441;    References  on  Washington  clays,  441; 
West  Virginia,  442;    Silurian,  442;    Devonian,  442;    Lower  Carboniferous,  442; 
Mauch  Chunk  shales,  442;    Carboniferous,  442;    Pottsville  series,  442;    Allegheny 
series,  445;    Clarion  clay,  445;    Kittanning  clays,  445;    Upper  Freeport  clay,  446; 
Conemaugh  series,  446;   Monongahela  series,  446;   Dunkard  or  Permo  Carbonifer- 
ous, 449;    Pleistocene,  449;    References  on  West  Virginia  clays,  451;    Wisconsin, 
451;    Residual  clays,  452;    Pre-Cambrian  residuals,  452;   Potsdam  shales,  452; 
Ordovician  limestone  residuals,   452;    Sedimentary  clays,  452;    Hudson  River 


CONTENTS 


PAGE 


shale,  452;  Pleistocene  clays,  455;  Lacustrine  deposits,  455;  Estuarine  clays, 
455;  Glacial  clays,  455;  References  on  Wisconsin  clays,  457;  Wyoming,  457; 
Bentonite,  457;  References  on  Wyoming  clays,  459. 


CHAPTER  VIII 

FULLERS'  EARTH 460 

Properties,  460;  Distribution  in  the  United  States,  461;  Georgia — Florida,  461; 
South  Carolina,  North  Carolina,  and  Virginia,  462;  New  York,  462;  Arkansas, 
462;  South  Dakota,  462;  California,  462;  Mining  and  uses,  466;  Production,  467. 


LIST  OF  ILLUSTRATIONS 


PLATE  PAGE 

I.  Bank  of  residual  clay  at  Christiansburg,  Va.,  showing  uneven  surface 

of  underlying  limestone 9 

II    Fig.  1.  Section  showing  beds  of  stratified  clay  overlain  by  glacial  drift .  .  15 
Fig.  2.  Bank  of  clay  showing  white  sand  on  right,  passing  into  a  black 

clay  on  the  left 15 

III.  Fig.  1.  Deposit  of  stony  glacial  clay 21 

Fig.  2.  Clay-pit  in  lignitic  Tertiary  formation,  Athens,  Texas.     Shows 

gently  dipping  layers 21 

IV.  Fig.  1.  Clay -bank  showing  carbonate  of  iron  concretions,  Reynolds  bank, 

Anne  Arundel  County,  Md 37 

Fig.  2.  Clay  concretions 37 

V.  Fig.  1.  Photomicrograph  of  kaolinite 43 

Fig.  2.  Washed  kaolin 43 

VI.  Photomicrograph  of  indianaite 45 

VII.  Fig.  1.  Section  showing  coal-bed  underlain  by  fire-clay 171 

Fig.  2.  Entrance  to  drift  in  fire-clay  seam,  which  is  overlain  by  limestone  171 

VIII.  Showing  method  of  working  clay  in  a  rectangular  pit     201 

IX.  Fig.  1.  Digging  clay  by  means  of  open  pits.     At  the  top  of  the  bank,  in 
the  background,  a  workman  is  driving  a  wedge  into  the  clay  in  order 

to  break  it  off.     The  clay  is  hauled  to  the  yards  in  carts 207 

Fig.  2.  Removing  the  overburden  from  a  shale- bed  by  hydraulicking. .  .  207 
X.  Fig.  1.  View  showing  portion  of  sand- troughs,  settling- tanks,  and  dry- 
ing-racks at  a  kaolin  washing-plant 215 

Fig.  2.  Filter  press  for  removing  water  from  washed  or  blunged  clays. 
The  portion  at  the  left  end  has  been  emptied  and  the  leaves  of  clay 
taken  from  it  are  on  the  car.  The  workman  is  just  removing  a  leaf 

of  clay  from  the  press 215 

XI.  Fig.  1.  Dry  pan  used  for  grinding  hard  clays,  shale,  and  brick 221 

Fig.  2.   Ring-pit  for  mixing  clays 221 

XII.  Fig.  1.  Wet  pan  for  grinding  and  mixing  clays  or  shales 225 

Fig.  2.  Cutting  table  of  stiff- mud  brick  machine 225 

XIII.  Dry-press  brick  machine 233 


xii  LIST  OF  ILLUSTRATIONS 

PLATE  PAGE 

XIV.  Fig.  1.  A  steam-power  re-press.     The  bricks  on  belt  are  being  brought 

from  the  stiff-mud  machine 237 

Fig.  2.  Setting  brick  for  a  scove-kiln 237 

XV.  Fig.  1.  Side  view  of  a  scove-kiln  for  burning  common   brick,  exterior 
daubed  with  wet  clay.     The  firing-holes  are  shown  at  bottom  of  one 

side 241 

Fig.  2.  Down-draft  kilns 241 

XVI.  Fig.  1.  Interior  view  of  circular  down-draft  kiln 243 

M?.  2.  Height  continuous  kiln 243 

XVII.  Fig.  1.  Molding  30-in.  sewer- pipe  in  pipe  press 249 

Fig.  2.  Some  forms  of  fireproofing  made  by  stiff-mud  machine 249 

XVIIL   Fig.  1.  Roofing-tile  press  for  molding  interlocking  tile 255 

Fig.  2.  Modeling  terra-cotta  objects 255 

XIX.  Fig.  1.  View  showing  method  of  setting  terra-cotta  in  kiln  for  burning.  .  259 
Fig.  2.  Partial  interior  view  of  a  pottery  kiln,  showing  saggers  in  which 

white  wares  are  burned 259 

XX.  Bergstrom  &  Bass  tile-press 267 

XXI.  Views  illustrating  the  process  of  turning  jars 273 

XXII.   Dipping  biscuit- ware  into  the  glazing  tubs 279 

XXIII.  Fig.  1.  Pit  of  Carboniferous  shale,  near  Birmingham,  Ala 287 

Fig.  2.  Tertiary  clays  (lone  formation)  used  for  brick,  terra-cotta,  etc., 

Lincoln 287 

XXTV.   Fig.  1.  Tertiary  clays  used  for  common  brick,  Los  Angeles,  Cal 291 

Fig.  2.  View  of  fire-clay  pits,  Golden,  Colo.     The  good  clay  has  been 

taken  out,  the  worthless  sandy  beds  left  standing 291 

XXV.  Fig.  1.  Kaolin- pit  at  West  Cornwall,  Conn 299 

Fig.  2.  White  clay  and  sands  of  Cretaceous  age,  overlain  by  Tertiary 

beds,  Rich  Hill,  near  Knoxville,  Ga 299 

XXVI.   Fig.  1.  Carboniferous  shale  used  for  paving-brick,  Galesburg,  111.     The 

excavating  is  done  with  a  steam  shovel 305 

Fig.  2.  View  in  Knobstone-shale  pit,  Crawfordsville,  Ind 305 

XXVTI.  Fig.  1.  Carboniferous  shale  for  paving-blocks,  near  Veedersburg,  Ind.. .  319 

Fig.  2    Cretaceous  shale,  Sioux  City,  la 319 

XXVIII.  Fig.  1.  Loess-bank,  Muscatine,  la 321 

Fig.  2.   Bank  of  Devonian  shale  used  for  paving-brick,  Cumberland,  Md.  321 
XXIX.  Fig.  1.  Coldwater  (Carboniferous)  shales  at  White  Rock,  near  Forest- 

ville,  Mich 343 

Fig.  2.  Carboniferous  shale,  used  for  paving-brick,  Flushing,  Mich 343 

XXX.  Fig.  1.   Deposit  of  calcareous  glacial  clay,  Ionia,  Mich 349 

Fig.  2.  Cretaceous  stoneware-clay,  Red  Wing,  Minn 349 

XXXI.   Fig.  1.  Photo  of  shaft-house  and  crushing-house  at  fire-clay  mine,  St. 

Louis 357 

Fig.  2.  Pit  of  Raritan  (Cretaceous)  clays,  Woodbridge,  N.  J 357 

XXXII.  Fig.  1.  Clay-loam  deposit  of  shallow  character,  west  of  Mount  Holly, 

N.  J 367 

Fig.  2.  Pleistocene  brick-clay,  Little  Ferry,  N.  J 367 

XXXIII.  Fig.  1.  Bank  of  Chemung  shale,  used  for  brick,  Corning,  N.  Y 379 

Fig.  2.   Bank  of  Pleistocene  clay,  overlain  by  sand,  Roseton,  N.  Y 379 


LIST  OF  ILLUSTRATIONS  xiii 

PLATE  PAGE 

XXXIV.  Fig.  1.  Kaolin-mine,  near  Webster,  N.  C.,  showing  mining  of  kaolin  by 

circular  pits 383 

Fig.  2.   Bank  of  Carboniferous  shale  near  Akron,  Ohio 383 

XXXV.  Fig.  1.  Kaolin-deposit  at  Upper  Mill,  Mount  Holly  Springs,  Pa 403 

Fig.  2.   White  sedimentary  clay,  Aiken  area,  S.  C 403 

XXXVI.  Bolivar  flint-clay,  Bolivar,  Pa.     This  clay  is  about  22  feet  thick  and 

overlain  by  impure  clay,  coal,  and  sandstone 409 

XXXVII.  Fig.  1.  Beds  of  Cretaceous  fire-clay,  southwest  of  Rapid  City,  S.  Dak..  .  417 
Fig.  2.  General  view  of  valley  at  Thurber,  Texas,  underlain  by  Carbon- 
iferous paving-brick  shale 417 

XXXVIII.  Fig.  1.   Bank  of  sewer- pipe  clay  in  Lignitic  (Tertiary)  formation,  Sas- 

pamco,  Texas.     Shows  electric  system  of  haulage 429 

Fig.  2.  Pit  in  Beaumont  clay,  Houston,  Texas.     The  walls  of  the  pit  are 

a  very  sandy  clay  underlying  the  other 429 

XXXIX.  Fig.  1.  View  of  kaolin-pit  near  Oak  Level,  Va.     The  ferruginous  clay 

walls  are  clearly  contrasted  to  the  white  kaolin 435 

Fig.  2.  General  view  of  kaolin  washing-plant  near  Oak  Level,  Va.     The 

crude  clay  is  washed  down  the  trough  from  the  mine 435 

XL.  Fig.  1.  Section   showing   diatomaceous   earth    (Miocene)    overlain    by 

Pleistocene  clay.     Dotted  line  shows  the  boundary 439 

Fig.  2.  Pleistocene  brick  and  tile-clay  underlying  terrace,  Oldfield  on 

James  River,  Va 439 

XLI.  Fig.  1.  Red-burning  brick-clay  bank  at  Freeman,  Wash 443 

Fig.  2.  Shale-bed  of  Mahoning  horizon,  Charleston,  W.  Va.     The  shale 

is  blue  and  red  with  some  fire-clay  mixed  through  it 443 

XLII.  Shale-pit  of  High  Grade  Shale  Brick  Co.,  Clarksburg,  W.  Va.     Coal- 
streak  near  top  is  the  redstone  coal  of  Monongahela  series 447 

XLIII.  Fig.  1.  Pit  of  estuarine  clay,  Fort  Atkinson,  Wis.     The  flat  area  is 

underlain  by  clay,  while  the  surrounding  low  hills  are  of  sand 453 

Fig.  2.  Pleistocene  clay,  Milwaukee,  Wis.     The  mound  in  middle  of  pit 

is  sand  and  is  left  standing 453 

XLIV.  Fig.  1.  Fullers'  earth  pit,  Quincy,  Fla.     Behind  it  are  the  drying-floors.  463 
Fig.  2.  Outcrop  of  Fullers'  earth,  northeast  of  Fairburn,  S.  Dak 463 

no.  PAGE 

1.  Section  showing  the  passage  of  the  fully  formed  residual  clay  on  the  surface  into 

the  solid   bed-rock  below.     A,  clay;    B,  clay  and  partly  decomposed  rock; 

C,  bed-rock  below,  passing  upward  into  rock  fragments  with  a  little  clay.  ...        7 

2.  Generalized  section  showing  three  possible  occurrences  of  kaolin  in  a  glaciated 

country.  1,  limestone;  2,  mica  schist;  3,  pegmatite;  4,  feldspathic  quartzite; 
5,  dark  gneiss;  6,  light  granite;  7,  dark  granite;  8,  kaolin,  protected  from 
glacial  erosion.  Arrow  indicates  direction  of  ice  movement 13 

3.  Generalized  section  showing  how  beds  may  vary  both  horizontally  and  vertically.     18 

4.  Section  showing  uneven  boundary  of  two  clay-beds,  due  to  erosion  of  one  before 

deposition  of  the  other 18 

5.  Section  of  folded  beds,  with  crest  worn  away,  exposing  different  layers 29 

6    Section  showing  strata  broken  by  parallel  fault-planes 29 

7.  Strata  broken  by  fault-plane  of  low  inclination 30 

8.  Section  of  horizontal  strata,  with  only  the  top  one  exposed  at  the  surface 30 


xiv  LIST  OF  ILLUSTRATIONS 

FIG.  PAGE 

9.  Section  showing  how  horizontal  beds  are  exposed  along  the  sides  of  a  valley. ...  31 

10.  Section  of  inclined  beds 31 

11.  Section  of  vertical  beds.     The  width  of  outcrop  is  the  same  as  the  actual  width 

of  the  bed 31 

12.  Horizontal  beds  with  several  layers  exposed  by  wearing  down  of  the  land  surface.  32 

13.  Inclined  strata,  showing  rise  of  the  bed  above  the  sea-level,  when  followed  up 

the  slope  or  dip 32 

14.  Outcrops  of  a  clay  on  two  sides  of  a  hill  and  its  probable  extension  into  the  sam^.  32 

15.  Section  showing  how  weathering  penetrates  a  clay-bed,  particularly  along  roots, 

cracks,  and  joint  planes 34 

16.  Section  showing  weathered  (yellow)  clay  where  the  overburden  is  least 34 

17.  Section  showing  occurrence  of  concretions  in  certain  layers 36 

18.  Curve  showing  effect  of  titanium  on  fusibility  of  clay 85 

19.  Changes  in  burning  a  black  clay  to  a  buff -colored  brick.     The  lightest  one  was 

not  removed  from  kiln  until  all  the  carbon  was  burned  off 89 

20.  Schoene's  apparatus  for  mechanical  analysis  of  clay 113 

21.  Hilgard's  apparatus  for  making  mechanical  analyses 114 

22.  Centrifugal  separator  for  mechanical  analyses 116 

23.  Drawing  showing  particles  of  a  Cape  May  clay 117 

24.  Drawing  of  an  Alloway  clay 118 

25.  Grains  of  sand  in  a  Clay  Marl  I,  M,  mica;    Q,  quartz;    Fy 

feldspar;  L,   lignite 119 

26.  Drawing  showing  bunches  of  kaolinite  (?)  plates  in  a  ball-clay  from  Edgar,  Fla.  119 

27.  Outline  and  dimensions  of  a  briquette  for  testing  the  tensile  strength  of  a  clay.  .  120 

28.  Riehle  machine  for  testing  tensile  strength 121 

29.  Fairbanks  tensile- strength  machine.     N,  clips  for  holding  briquettes;   P,  screw 

for  applying  strain  to  balance- lever  C;  F,  bucket  to  hold  shot  fed  in  through 

/  from  the  hopper  K;  J,  automatic  cut-off 122 

30.  Curve  showing  relation  between  fineness  of  grain  of  non-plastic  material  and 

tensile  strength  of  clay  mixtures 124 

31.  Curves  showing  relation  of  texture  to  tensile  strength 126 

32.  Seger's  volumeter  for  determining  porosity  and  specific  gravity 133 

33.  Diagram  showing  effect  of  silica  on  the  fusion-point  when  mixed  with  alumina 

and  with  kaolin,  from  Seger's  experiments 141 

34.  Seger  cones  used  for  determining  heat  effects  in  kilns.     Nos.  7  and  8  were  com- 

pletely melted;    No.  10  was  slightly  softened;   No.  12  was  unaffected;  No.  9 
was  bent  completely  over,  but  not  melted.     The  fusing-point  of  cone  9   was 

reached 148 

35.  Section  of  kiln  showing  method  of  placing  Seger  cones 152 

36.  Map  showing  kaolin  and  ball-clay  deposits  of  United  States  east  of  the  Mississippi 

River 166 

37.  Diagram  showing  effects  of  silica  on  fusibility  of  kaolin 174 

38.  Formation  of  spring  due  to  ground- water  following  a  clay-layer 200 

39.  Formation  of  a  spring  due  to  a  layer  of  cemented  sand 200 

40.  Formation  of  a  pond  due  to  a  clay- bed  beneath  a  depression. 200 

41.  Section  of  pit  working  in  Middlesex  district 206 

42.  Pug-mill  for  tempering  clay 223 

43.  A  soft-mud  brick-machine 227 


LIST  OF  ILLUSTRATIONS  XV 

FIG.  PAGE 

44.  Manufacture  of  brick  by  stiff- mud  process 229 

45.  Tunnels  for  drying  bricks  and  other  structural  clay-products 235 

46.  Side  elevation  of  sewer-pipe  press 245 

47.  Front  elevation  of  sewer-pipe  press 246 

48.  Graphic  representation  of  composition  and  fusibility  of  some  domestic  fire-brick.  253 

49.  Section  across  Connecticut  Valley,  showing  relations  of  the  clays  and  other  Pleis- 

tocene deposits. 294 

50.  Map  of  a  portion  of  Georgia,  showing  location  of  clay -works  in  coastal  plain  area.  302 

51.  Map  of  Indiana,  showing  a  real  distribution  of  Goal-measure  shales  and  Knob- 

stone  shales 308 

52.  Section  near  Glen  Mine,  Coal  Bluff,  Ind.,  showing  association  of  coals  under 

clays,  etc 311 

53.  Map  of  Iowa,  showing  distribution  of  clay- bearing  formations,  and  location  of 

clay-  and  shale-pits 317 

54.  Map  of  Missouri,  showing  distribution  of  clay-  bearing  formations,  and  location 

of  clay-pits 353 

55.  Map  showing  distribution  of  Missouri  kaolins 354 

56.  Section  of  a  Missouri  flint-clay  deposit. 355 

57.  Map  of  New  Jersey,  showing  distribution  of  important  clay-bearing  formations.  365 

58.  Map  of  Northeastern  States,  showing  distribution  of  clay- bearing  formations. .  .   377 

59.  Map  of  Ohio,  showing  distribution  of  clay-  and  shale-bearing  formations 391 

60.  Section  of  Barren  Measures  opposite  Steubenville,  Ohio 396 

61.  Vertical  sections  near  New  Brighton,  Pa. 408 

62.  Section  of  Barren  Measures  in  Pittsburg  region,  Pennsylvania 412 

63.  Map  of  eastern  Texas,  showing  distribution  of  clay- bearing  formations. 425 

64.  Map  of  Wisconsin,  showing  distribution  of  clay- bearing  formations 451 

65.  Map  of  Benton  formation  in  Wyoming • 459 


LIST  OF  ABBREVIATIONS   USED 


Amer.  Geol.  —f  American  Geologist. 

Amer.  Jour.  Sci.  =  American  Journal  of  Science. 

Ann.  des  M ines  =  Annales  des  Mines  de  Paris. 

Bdhm.  Ges.  Wiss.  =  Bohmische  Gesellschaf t  fiir  Wissenschaften. 

Bull.  Geol.  Soc.  Amer.  =  Bulletin  Geological  Society  of  America. 

Comptes  rend.  —  Comptes  rendus  de  la  Academie  des  Sciences  de  Paris. 

Dingl.  polyt.  Jour.  =  Dingler's  Polytechnisches  Journal. 

Jour.  Geol.  = Journal  of  Geology. 

Jour.  prak.  Chem.  =  Journal  iiir  praktische  Chemie. 

M  in.  Mag.  =  Mineralogical  Magazine. 

Min.  Tasch.  =  Mineralogisches  Taschenbuch. 

Naturhist.  Ver.  J?o7w  =  ]STaturhistorischen  Vereins  Bonn. 

Neues  Jahrb.  =  Neues  Jahrbuch  fiir  Mineralogie,  Geologie  und  Palaeontologie. 

Pogg.  Ann.  =  Poggendorfs  Annalen. 

Phil.  Trans.  =-  Philosophical  Transactions. 

Quart.  Jour.  Chem.  Soc.  =  Quarterly  Journal  of  the  Chemical  Society  of  London. 

Royal  Agric.  Soc.  Jour.  =  Journal  of  the  Royal  Agricultural  Society  of  London. 

Seger  Ges.  Schrift.  =  Seger's  Gesammelte  Schriften. 

Syst.  Min.  =  Dana's  System  of  Mineralogy = 

Tscherm.  Mitth.  =  Tschermak's  Mineralogische  und  Petrographische  Mittheilungen. 

Trans.  Amer.  Ceram.  Soc.  =  Transactions  American  Ceramic  Society. 

Trans.  Amer.  Inst.  Min.  Eng.  =  Transactions  American  Institute  Mining  Engineers. 

Trans.  Eng.  Cer.  Soc.  =  Transactions  English  Ceramic  Society. 

Trans.  N.  Y.  Acad.  Sci.  =  Transactions  New  York  Academy  of  Sciences. 

Zeitschr.  anorg.  Chem.  =  Zeitschrift  fur  anorganische  Chemie. 

Zettschr.  d.  d.  Geol.  Ges.  =  Zeitschrift  der  deutschen  Geologischen  Gesellschaft. 

Zeitschr.  f.  Kryst.  u.  Min.  =  Zeitschrift  fiir  Krystallographie  und  Mineralogie. 

Zeitschr.  prak.  Geol.  =  Zeitschrift  fiir  praktische  Geologie. 

xvi 


or  THF 
UNIVERSITY 

OF 


CLAYS 

THEIR  OCCURRENCE,  PROPERTIES,  AND  USES 


CHAPTER  I 
ORIGIN  OF  CLAY 

Definition. — Clay  is  the  term  applied  to  those  earthy  materials 
•occurring  in  nature  whose  most  prominent  property  is  that  of  plasticity 
when  wet.  On  this  account  they  can  be  molded  into  almost  any  desired 
shape,  which  is  retained  when  dry.  Furthermore,  if  heated  to  redness, 
or  higher,  the  material  becomes  hard  and  rock-like.  Physically,  clay  is 
made  up  of  a  number  of  small  particles  mostly  of  mineral  character, 
ranging  from  grains  of  coarse  sand  to  those  which  are  of  microscopic 
size,  or  under  one  one-thousandth  of  a  millimeter  in  diameter.  Minera- 
logically,  it  consists  (1)  of  many  different  mineral  fragments,  some  of 
them  fresh,  but  others  in  all  stages  of  decay,  and  representing  chemically 
many  different  compounds,  such  as  oxides,  carbonates,  silicates,  hydrox- 
ides, etc.;  (2)  of  colloidal  material  which  might  be  of  either  organic  or 
mineral  character.1 

These  points  are  discussed  in  more  detail,  however,  on  a  later  page 
(see  Minerals  in  Clays,  Physical  properties  and  Chemical  composition). 

Weathering  processes  involved. — Clays  are  always  of  secondary  ori- 
gin and  result  primarily  from  the  decomposition  of  other  rocks,  very 
frequently  from  rocks  containing  feldspar,  so  that  for  this  reason  many 
writers  have  intimated  that  it  was  always  derived  from  feldspathic  rocks. 
There  are  some  rock  species,  however,  that  contain  no  feldspar  (such  as 
serpentine),  and  others  with  very  little  (as  some  gabbros),  which,  on 
weathering,  produce  some  of  the  most  plastic  clays  known. 

1  H.  Ries,  Md.  Geol.  Surv.,  IV,  251,  1902;  A.  S.  Cushman,  Jour.  Amer.  Chem. 
Soc.,  XXV,  5. 


2  CLAYS 

In  order  to  trace  the  changes'  occurring  in  the  formation  of  clay  we 
may  take  the  case  of  a  rock  like  granite. 

When  such  a  mass  of  rock  is  exposed  to  the  weather,  minute  cracks 
are  formed  in  it,  due  to  the  rock  expanding  when  heated  by  the  sun 
and  contracting  when  cooled  at  night,  or  they  may  be  joint  planes  formed 
by  the  contraction  of  the  rock  as  it  cooled  from  a  molten  condition.  Into 
these  cracks  the  rain-water  percolates  and,  when  it  freezes  in  cold  weather, 
it  expands,  thereby  exerting  a  prying  action,  which  further  opens  the 
fissures,  or  may  even  wedge  off  fragments  of  the  rock.  Plant-roots  force 
their  way  into  these  cracks,  and,  as  they  expand,  supplement  the  action 
of  the  frost,  thus  further  aiding  in  the  breaking  up  of  the  mass.  This 
process  alone,  if  kept  up,  may  reduce  the  rock  to  a  mass  of  small  angular 
fragments,  or  even  a  mass  of  sand. 

The  rock  having  been  opened  up  by  disintegrate  forces,  the  silicates 
are  next  attacked  by  the  surface-waters,  although  those  exposed  on  the 
surface  of  the  stone  may  already  have  begun  to  change. 

It  has  usually  been  supposed  that  the  decomposition  of  the  silicates 
in  the  rock,  such  as  feldspar,  is  caused  chiefly  by  the  dissolved  carbon 
dioxide,  which  is  probably  always  present  in  the  percolating  waters, 
and  this  view  was  advanced  by  Forschammer  as  early  as  1835, 1  as  well 
as  by  other  writers  later;2  but,  as  pointed  out  by  Cameron  and  Bell,3 
this  is  very  doubtful,  in  view  of  the  fact  that  many  of  the  minerals  found 
in  rocks  are  known  to  be  soluble  in  water  alone,  although  their  solution 
may  take  place  but  slowly.  The  water,  moreover,  is  believed  to  react 
with  or  hydrolyze  them,  as  is  shown  by  the  fact  that  an  alkaline  reaction 
can  be  obtained  with  phenolphthalein,  after  treating  powdered  minerals 
with  water  free  from  dissolved  carbon  dioxide. 

The  rate  of  solubility  varies,  of  course,  with  the  different  minerals ,. 
the  magnesium-bearing  micas  being  more  soluble  than  muscovite,  and 
albite  more  so  than  orthoclase,  with  oligoclase  between.4  Clarke  5  found 
that  muscovite,  lepidolite,  phlogopite,  orthoclase,  oligoclase,  albite,  leu- 
cite  nephelite,  cancrinite  spodumene,  scapolite,  and  many  zeolites,  all 
dissolve  in  water,  giving  an  alkaline  reaction,  and  the  same  has  been 
shown  of  others.6 

1  Pogg.  Ann.,  XXXV,  p.  354,  1835. 

'Rogers,  Amer.  Jour.  Sci..  V,  p.  404,  1848;  Bischof,  Naturhist.  Ver.  Bonn, 
XII,  p.  308,  1855;  Daubree,  Compt.  ren.,  LXIV,  p.  339,  1867;  Miller,  Tscherm. 
Mitth.,  1877,  p.  31. 

3  Bur.  of  Soils,  Bull.  30,  p.  16,  1905. 

4  Merrill,  Rocks,  Rock-weathering  and  Soils,  p.  234,  1897. 
6  U.  S.  Geol.  Surv.,  Bull.  167,  p.  156,  1900. 

6  See  Bull.  30,  Bur.  of  Soils,  for  numerous  references  on  this  subject. 


ORIGIN  OF  CLAY  3 

The  action  of  water  on  orthoclase  is  assumed  to  be  somewhat  accord- 
ing to  the  following  formula  l  : 


The  potassium  hydrate  thus  formed  may  unite  with  carbon  dioxide 
to  form  either  a  carbonate  or  bicarbonate  of  potash,  or  it  is  possible 
that  it  may  unite  with  other  acids,  forming  salts  more  soluble  than  the 
orthoclase  in  the  hydrolyzed  acid. 

The  HAlSi3Os  formed  is  apparently  unstable,  and  may  lose  some  of 
its  quartz,  resulting  in  the  formation  of  kaolinite,  pyrophyllite,  or  dia- 
spore,  but  the  first  of  these  appears  to  be  more  commonly  formed  in 
the  weathering  of  feldspar. 

Kaolinization.  —  This  alteration  of  the  feldspar  is  termed  kaolinization, 
and  the  mineral  kaolinite  is  always  of  secondary  character.  The  changes 
which  take  place  in  the  alteration  of  several  species  of  feldspar  may  be 
given  as  follows  : 


SiO2 

A1203 

K2O 

H20 

% 

Orthoclase  

64.86 

18.29 

16.85 

100.00 

Lost  

43.24 

16.85 

60.09 

Taken  up  

6.45 

6.45 

Kaolinite  

21.62 

18.29 



6.45 

46.36 

Albite  

Si02 
68.81 

A1203 
19.40 

Na20 
11.79 

H20 

% 
100.00 

Lost  

45.87 

11.79 

57.66 

Taken  up  



6.85 

6.85 

Kaolinite  

22.94 

19.40 

6.85 

49.10 

Anorthite  

SiO2 
43.30 

A1203 
36.63 

CaO 
20.07 

H2O 

% 
100.00 

Lost  

20  07 

20.07 

Taken  up  



12.92 

12.92 

Kaolinite  

43.30 

36.63 

12.92 

92.85 

It  will  be  seen  from  this  that  both  the  orthoclase  and  plagioclase 
might  yield  kaolinite;  in  fact  the  plagioclase  varieties  decompose  more 
readily  than  orthoclase.2 

Vogt3  has  recorded  an  occurrence  of  kaolin  near  Josingfjord,  atEker- 

1  Cameron  and  Bell,  1.  c.,  p.  18. 

2  Ries,  Kaolins  and  fire-clays  of  Europe,  U.  S.  Geol.  Surv.,  19th  Ann.  Rept., 
pt.  VI  (ctd.),  p.  377,  1898;  Leimberg,  Zeitsch,  d.  d.  Geol.  Ges.,  Vol.  35,  1883;  Rosier, 
Neues  Jahr.,  Beil.  Bd.  XV,  2d  Heft,  p.  231. 

3  Amer.  Inst.  Min.  Eng.,  Trans.,  XXXI,  p.  151,  1902. 


CLAYS 


sund-Soggendal,  Norway,  which  is  formed  from  labradorite,  the  different 
stages  in  the  change  being  indicated  by  the  following  analyses : 


Labra- 
dorite. 

Labradorite 
partly  kaoli- 
nized. 

Massive  kaolin,  more  or  less  pure. 
Kao- 

litiito 

I 

II 

I 

II 

III 

IV 

V 

Silica  (SiO2)  
Alumina  (A^Oa)  
Iron  oxide  (Fe2Oa)  .  . 
Lime  (CaO)  
Magnesia  (MgO)  
Potash  (KijO)  
Soda  (Na2O)  
Water  (HaO) 

54.5 
27.0 
2  5 
9.0 
10 
1  0 
5.0 

50  03 
28  60 
1.62 
4  21 
2.95 

[    1  00 
11  90 

49.16 
29  60 
1.88 
3.47 
1.67 

undet. 
13  63 

48.16 
29.45 
3.40 
.68 
.49 

undet. 
16.38 

48.06 

f  38.57 

1 

}•  undet 

J 

12.95 

47.83 
1  34  .  53 
1    1.70 
1       .48 
}•      .59 
J  undet 

13  76 

47  72 
37.40 
1.59 
.23 
.11 
44 
.76 
11.66 

46  85    46.50 
37.56    39  56 
1.00 
tr. 
tr. 

[•  undet1 
14  44     13.94 

Total 

100  6 

100.31 

(99.41) 

(99.01) 

(99  58) 

(98.89) 

99.91 

(99  85)  100  00 

Prof.  Vogt  believes  that  the  kaolinization  here  is  due  to  the  action  of 
carbonic-acid  waters,  because  calcite  occasionally  occurs  with  the  kaolin- 
However,  from  what  has  been  said  on  page  2,  the  presence  of  this  min- 
eral would  not  necessarily  show  that  the  acid  above  mentioned  had 
assisted  in  the  decomposition  of  the  feldspar,  but  simply  that  it  had 
united  with  the  lime  set  free  during  the  breaking  up  of  the  labradorite. 

While  it  is  probable  that  other  silicates,  such  as  hornblende  or  augite, 
yield  a  hydrous  aluminum  silicate,  it  is  not  known  that  it  is  kaolinite,1 
but  their  decomposition  no  doubt  proceeds  in  a  manner  similar  to  that 
of  feldspar. 

Vogt,2  on  the  other  hand,  states  that  hornblende,  augite,  beryl,  topaz, 
etc.,  are  known  to  be  occasionally  converted  into  kaolinite,  but  gives 
no  evidence. 

Quartz,  although  apparently  resistent,  is  not  left  untouched,  for  it 
too  is  slightly  soluble,  but,  aside  from  that  originally  present  in  the  rock, 
silica  may  have  been  liberated  during  the  decomposition  of  some  of  the 
silicates,  such  as  feldspar. 

It  has  been  found  that  in  soils,  and  the  same  may  be  said  of  clays, 
quartz  has  accumulated  in  relatively  large  proportions.  It  may  be 
present  as  quartz,  amygdaloidal  silica,  or  perhaps  other  forms.  There 
is,  however,  a  tendency  for  it  to  be  gradually  changed  over  into  other 
forms  of  quartz  through  solution  and  redeposition.3 


1  Merrill,  Rocks,  Rock-weathering  and  Soils,  p.  21,  1897.    • 

2  Problems    in  the  Geology  of  Ore  Deposits,  Trans.  Amer.  Inst.    Min.  Eng., 
XXXI,  p.  151,  1902. 

3  Hayes,  Bull.  Geol.  Soc.  Amer.,  VIII,  p.  213,  1897,  and  Jour.  Geol.,  V,  p.  319, 

1897. 


ORIGIN  OF  CLAY  5 

While  there  is  undoubtedly  lack  of  absolute  proof  that  other  silicates 
than  feldspar  yield  kaolinite,  all  clays  appear  to  contain  a  variable  amount 
of  some  hydrated  silicate  of  aluminum,  which  may  be  present  in  some 
quantity,  since  it  is  a  highly  insoluble  natural  compound;  and  even 
though  the  statement  is  frequently  made  that  this  silicate  is  the  mineral 
kaolinite,  the  fact  is  at  times  somewhat  difficult  of  proof;  indeed  the 
evidence  is  clearly  against  it  in  some  cases. 

This  hydrated  aluminum  silicate  is- sometimes  referred  to  as  the  clay 
substance  or  clay  base.1 

Kaolinization  by  pneumatolysis. — Aside  from  the  kaolinization  of 
feldspar  by  the  ordinary  processes  of  weathering  it  seems  possible,  and 
even  probable,  that  its  decomposition  may  have  been  brought  about  by 
the  action  of  mineralizing  vapors,  as  at  Cornwall,  Eng.,  where  it  was 
found  that  the  feldspar  of  the  granite  on  both  sides  of  the  tin  veins  had 
been  kaolinized.  This  change  is  attributed  to  the  action  of  fluoric  vapors, 
whose  presence  is  pretty  clearly  indicated  by  the  finding  of  such  minerals 
as  tourmaline  and  topaz. 

That  such  a  process  is  possible  is  shown  by  J.  H.  Collins,2  who  ex- 
posed feldspar  to  the  action  of  hydrofluoric  acid.  The  feldspar,  accord- 
ing to  Mr.  Collins,  was  converted  into  hydrated  silicate  of  alumina,  mixed 
with  soluble  fluoride  of  potassium,  while  pure  silica  was  deposited  on 
the  sides  of  the  tube. 

With  such  treatment  the  orthoclase  yielded  more  readily  than  either 
albite  or  oligoclase.  The  following  analyses  show  the  effect  of  96  hours' 
treatment  of  orthoclase  with  hydrofluoric  acid  at  60°  F.: 

I.  II.  III. 

Silica  (SiO8) 63.70  49.20  44.10 

Alumina  (A12O3) 19-76  35.12  40.25 

Potash  (K.O) 13.61  .12  .25 

Soda  (Na2O) 2.26  tr.  tr. 

Ferric  oxide  (Fe2O3) .71  tr.  tr. 

Water  (H2O) tr.  14.20  15.01 


100.04       98.64       99.61 


I  is  the  original  feldspar. 
II  is  inner  layer  of  altered  feldspar. 
Ill  is  outer  layer  of  altered  feldspar. 


1  The  term  is  now  rather  loosely  used,  however,  and  in  impure  clays  includes 
practically  all  of  the  very  finest  particles. 
2Min.  Mag.,  1887,  VII,  p.  213. 


^  CLAYS 

From  the  analysis  it  will  be  seen  that  the  composition  of  the  outer 
layer  simply  approximates  that  of  kaolinite. 

The  artificial  clay  thus  produced,  when  examined  under  the  micro- 
scope, resembled  washed  kaolin.  It  shoxved  no  hexagonal  scales,  but 
contained  a  number  of  minute  colorless  cubes  which  are  supposed  to  be 
fluorspar. 

The  theory  advanced  by  Mr.  Collins  was  earlier  suggested  by  Von 
Buch  and  Daubree.1 

The  former  early  observed  the  constant  occurrence  of  kaolin  with 
minerals  containing  fluorin,  and  suggested  that  the  kaolin  of  Halle, 
dermany,  owed  its  origin  to  hydrofluoric  acid.2 

Daubree  considered  that  the  kaolin  near  St.  Austell  in  Cornwall,3 
Central  France,  and  the  Erzgebirge  must  have  had  a  similar  origin. 

The  formation  of  kaolin  by  other  causes  than  surface  agencies  has 
loeen  referred  to  by  B.  von  Inkey  and  Semper  as  a  product  of  propyliti- 
zation  in  some  cases.4  Cross  and  Penrose  5  have  sought  to  suggest  a 
pneumatolytic  origin  for  the  kaolin  found  in  some  of  the  Cripple  Creek, 
Colo.,  mines,  but  Ransome  and  Lindgren  6  have  rather  disputed  this. 

If  Mr.  Collins'  theory  be  correct,  the  kaolin  deposits  should  extend 
to  great  depths,  but  if  the  kaolinization  be  due  to  weathering,  then  we 
should  encounter  undecomposed  feldspar  at  the  limit  to  which  weather- 
ing has  reached.  In  Cornwall  the  kaolin  mines,  which  are  probably  the 
largest  in  the  world,  have  reached  a  depth  of  over  400  feet  without  the 
"kaolin  giving  out,  while  at  Zettlitz  in  Bohemia  a  similar  depth  has  been 
proven  with  the  same  result.  The  latter  locality  is  one  of  thermal  ac- 
tivity. In  these  two  instances  the  theory  just  mentioned  seems  to  be 
Tery  reasonable.  There  are  many  localities,  however,  where  the  kaolin 
decreases  with  the  depth,  passing  into  the  undecomposed  feldspar,  as 
is  the  case,  for  example,  in  North  Carolina,  where  the  fresh  feldspar  is 
met  at  a  depth  of  60  to  120  feet,  in  Pennsylvania,  and  also  in  Delaware. 
IVIore  recently  Rosier  7  has  advanced  the  view,  on  wrhat  seems  to  the  writer 
rather  insufficient  evidence,  that  the  kaolinization  of  feldspars  is  never 


1  Annales  des  mines,  XX,  1841. 

2  Min.  Tasch.,  1824.     The  writer  can  state  from  personal  examination  that  the 
Halle  kaolins  were  formed  by  ordinary  weathering. 

3  Etudes  synthetiques  de  Geologic  Experimental,  1879. 

4  Nagyag  u.  seine  Lagerstatten,  Budapest,  1885. 
5U.  S.  Geol.  Surv.,  16th  Ann.  Kept.,  Pt.  IT,  p.  160. 

6  U.  S.  Geol.  Surv.,  Bull.  254,  p.  21,  1904. 

7  H.  Rosier  Beitrase  zur  kenntniss  der  Kaolinlagerstatten,  Neues  Jahrb.  f.  Min., 
£eol.  u.  Pal.,  XV.  Beilage-Band,  2d  Heft.  pp.  231-393. 


ORIGIN   OF  CLAY  7 

due   to   atmospheric   action,  but  to    post-volcanic    pneurruitolytic   and 
pneumatohydatogeriic  processes. 

The  very  fact  that  many  of  our  kaolins  pass  into  undecomposed  feld- 
spar or  feldspathic  rock  when  the  limit  of  weathering  is  reached  shows 
the  incorrectness  of  such  a  broad  statement.1 

Residual  Clay 

Where  the  clay  is  thus  found  overlying  the  rock  from  which  it  was 
formed,  it  is  termed  a  residual  clay,  because  it  represents  the  residue 
of  rock  decay,  and  its  grains  are  more  or  less  insoluble. 

If  now  a  granite  which  is  composed  chiefly  of  feldspar  decays  under 
weathering  action,  the  rock  will  be  converted  into  a  clayey  mass,  with 
quartz  and  mica  scattered  through  it.  Remembering  that  the  weather- 
ing began  at  trhe  surface  and  has  been  going  on  there  for  a  longer  period 
than  in  deeper  portions  of  the  rock,  we  should  expect  to  find,  on  digging 
downward  from  the  surface,  (.4)  a  layer  of  fully  formed  clay,  (B)  below 
this  a  poorly  defined  zone  containing  clsy  and  some  partially  decomposed 
rock  fragments,  (0)  a  third  zone,  with  some  clay  and  many  rock  fragments, 
grading  downward  into  the  solid  bed-rock.  (Fig.  1.)  In  other  words. 


FIG.  1. — Section  showing  the  passage  of  the  fully  formed  residual  clay  on  the  sur- 
face into  the  solid  bed-rock  below.  A,  clay;  B,  clay  and  partly  decomposed 
rock;  C,  bed-rock  below,  passing  upward  into  rock  fragments  with  a  little  clay. 

there  is  usually  a  gradual  transition  from  the  fully  formed  clay  at  the 
surface  into  the  parent  rock  beneath.  The  only  exception  to  this  is  found 
in  clays  derived  from  limestone,  where  the  passage  from  dry  to  rock  is 

1  In  this  connection,  see  G.  P.  Merrill,  What  Constitutes  a  Clay,  Amer.  Geol. 
XXX,  Nov.  1902,  and  H.  Ries,  Origin  of  Kaolin,  Trans.  Amer.  Ceramic  Soc., 
II,  p.  93,  1900. 


8  CLAYS 

sudden.  The  reason  for  this  is  that  the  change  from  limestone  into  clay 
does  not  take  place  in  the  same  manner  as  granite.  Limestone  consists 
of  carbonate  of  lime,  or  carbonate  of  lime  and  magnesia,  with  a  variable 
quantity  of  clay  impurities,  so  that  when  the  weathering  agents  attack 
the  rock,  the  carbonates  are  dissolved  out  by  the  surface-waters,  and 
the  insoluble  clay  impurities  are  left  behind  as  a  mantle  on  the  undis- 
solved  rock,  the  change  from  rock  to  clay  being,  therefore,  a  sudden  one, 
and  not  due  to  a  gradual  breaking  down  of  the  minerals  in  the  rock,  as 
in  the  case  of  granite. 

Kaolin. — A  residual  clay  derived  from  a  rock  composed  entirely  of 
feldspar,  or  one  containing  little  or  no  iron  oxide,  is  usually  white  and 
therefore  termed  a  kaolin;  deposits  of  this  type  may  contain  a  high 
percentage  of  the  mineral  kaolinite,1  this  being  assumed  because,  after 
cashing  the  sand  out  of  such  materials,  the  silica,  alumina,  and  water 
in  the  remaining  portion  are  in  much  the  same  ratios  as  in  kaolinite, 
although,  as  previously  mentioned,  other  aluminous  silicates  may  at 
times  be  present. 

A  clay  made  up  entirely  of  kaolinite  is  sometimes  termed  a  "pure" 
clay,  but  since  the  term  clay  refers  to  a  physical  condition  and  not  a 
definite  chemical  composition,  it  would  perhaps  be  more  correct  to 
term  kaolin  the  simplest  form  of  clay. 

There  are  clays  made  up  almost  entirely  of  other  hydrous  aluminum 
silicates  than  kaolinite,  which  are  also  termed  kaolins,  as  the  indianaite 
of  Indiana,  or  the  halloysite  of  Alabama. 

A  deposit  of  pure  kaolinite  has  not  thus  far  been  found  in  nature 
though  some  very  nearly  pure  occurrences  are  known.  While  the  term 
kaolin  is  sometimes  applied  to  any  residual  clay,  the  writer  believes  that 
this  designation  should  be  restricted  to  white-burning  residual  clays,  a 
usage  which  is  wide-spread  but  has  not  become  universal.  The  name 
kaolin  is  a  corruption  of  the  Chinese  Raiding,  which  means  high  ridge,  and 
is  the  name  of  a  hill  near  Jauchau  Fu,  where  the  mineral  is  obtained.2 

In  this  connection  it  is  interesting  to  note  that,  according  to  Richt- 
hofen,3  the  rock  from  which  the  King-te-chin  porcelain  is  made  is  not 
true  kaolin,  but  a  hard  jade-like  greenish  rock  which  occurs  between 
beds  of  slate.  He  states:  "This  rock  is  reduced,  by  stamping,  to  a  white 
powder,  of  which  the  finest  portion  is  ingeniously  and  repeatedly  sep- 

1  The  terms  kaolinite,  referring  to  the  mineral,  and  kaolin,  referring  to  the  rock 
mass,  are  often  carelessly  confused  even  by  scientific  writers,  although  there  seems 
to  be  little  excuse  for  so  doing. 

2  Dana,  System  of  Min.,  1892,  p.  687. 
s  Amer.  Jour.  Sci.,  1871,  p.  180. 


0  OS 

las 


S  3 

73    o 

S£ 
J 


ORIGIN   OF  CLAY  11 

arated.  This  is  then  molded  into  small  bricks.  The  Chinese  distinguish 
chiefly  two  kinds  of  this  material.  Either  of  them  is  sold  in  King-te-chin 
in  the  shape  of  bricks,  and  as  either  is  a  white  earth,  they  offer  no  visible 
differences.  They  are  made  at  different  places,  in  the  manner  described, 
by  pounding  hard  rock,  but  the  aspect  of  the  rock  is  nearly  alike  in  both 
cases.  For  one  of  these  two  kinds  of  material  the  place  Kaoling  ('high 
ridge')  was  in  ancient  times  in  high  repute,  and,  though  it  has  lost  its 
prestige  since  centuries,  the  Chinese  still  designate  by  the  name  'Kao- 
ling' the  kind  of  earth  which  was  formerly  derived  from  there,  but  is 
now  prepared  in  other  places.  The  application  of  the  name  by  Berzelius 
to  porcelain  earth  was  made  on  the  erroneous  supposition  that  the  white 
earth  which  he  received  from  a  member  of  one  of  the  embassies  (I  think 
Lord  Amherst)  occurred  naturally  in  this  state.  The  second  kind  of 
material  bears  the  name  Pe-tun-tse  ('white  clay')." 

The  following  analyses  1  show  the  average  composition  of  (I)  the 
natural  material  from  King-te-chin,  such  as  is  used  in  the  manufacture 
of  the  finest  porcelain;  (II)  that  from  the  same  locality  used  in  the  so- 
called  blue  Canton  ware;  (III)  that  of  the  English  Cornwall  stone; 
(IV)  washed  kaolin  from  St.  Yrieux,  France;  and  (V)  washed  kaolin 
rom  Hockessin,  Del. 

I.  II.  III.  IV.  V. 

Silica  (SiO2) 73.55  73.55  73.57  48.68  48.73 

Alumina  (A12O3) 21.09  18.98  16.47  36.92  37.02 

Ferric  oxide  (Fe2O3) .27           .79 

Lime  (CaO) 2.55  1.58  1.17           .16 

Magnesia  (MgO) .15  1.08  .21  .52  .11 

Potash  (K,0) .461  -  84  5g  /  .41 

.Soda(Na20) 2.09/  1-04 

Water  (H2O) 2.62  1.96  2.45  13.13  12.83 

Total 99.62  99.70  99.98  99.83         100.00 

The  above  analyses  show  a  most  striking  difference  between  the  two 
washed  kaolins  and  the  Chinese  clay  and  Cornwall  stone. 

Form  of  residual  deposits. — The  form  of  a  residual  clay  deposit, 
which  is  also  variable,  depends  on  the  shape  of  the  parent  rock.  Where 
the  residual  clay  has  been  derived  from  a  great  mass  of  granite  or  other 
clay-yielding  rock,  the  deposit  may  form  a  mantle  covering  a  consider- 
able area.  On  the  other  hand,  some  rocks,  such  as  pegmatites  (feldspar 
and  quartz),  occur  in  veins,  that  is,  in  masses  having  but  small  width  as 
compared  with  their  length,  and  in  this  case  the  outcrop  of  residual  clay 
along  the  surface  will  form  a  narrow  belt. 

1  G.  P.  Merrill,  Non-metallic  Minerals,  p.  224,  1901. 


12  CLAYS 

Clay  derived  from  a  rock  containing  much  iron  oxide  will  be  yellow 
red,  or  brown,  depending  on  the  iron  compounds  present.     Between  the 
white  clays  and  the  brilliantly  colored  ones  others  are  found  represent- 
ing all  intermediate  stages,  so  that  residual  clays  vary  widely  in  their 
color. 

The  depth  of  a  deposit  of  residual  clay  will  depend  on  climatic  con- 
ditions, character  of  the  parent  rock,  topography,  and  location.  Rock 
decay  proceeds  very  slowly,  and  in  the  case  of  most  rocks  the  rate  of 
decay  is  not  to  be  measured  in  months  or  years,  but  rather  in  centuries. 
Only  a  few  rocks,  such  as  some  shales  or  other  soft  rocks,  change  to  clay 
in  an  easily  measurable  time.  With  other  things  equal,  rock  decay 
proceeds  more  rapidly  in  a  moist  climate,  and  consequently  it  is  in  such 
regions  that  the  greatest  thickness  of  residual  materials  is  to  be  looked 
for.  The  thickness  might  also  be  affected  by  the  character  of  the  parent 
rock,  whether  composed  of  easily  weathering  minerals  or  not.  Where 
the  slope  is  gentle  or  the  surface  flat,  much  of  the  residual  clay  will  re- 
main after  being  formed,  but  on  steep  slopes  it  will  soon  wash  away. 

In  some  cases  the  residual  materials  are  washed  but  a  short  distance 
and  accumulate  on  a  flat  or  very  gentle  slope  at  the  foot  of  the  steeper 
one,  forming  a  deposit  not  greatly  different  from  the  original  ones,  al- 
though they  are  not,  strictly  speaking,  residual  clays. 

Distribution  of  residual  clays. — Residual  clays,  usually  of  ferruginous 
character,  are  found  in  many  portions  of  the  United  States,  but  reach 
their  maximum  development  in  that  portion  lying  east  of  the  Mississippi 
and  south  of  the  southern  margin  of  the  ice-sheet  of  the  glacial  epoch. 

North  of  the  terminal  moraine  they  are  found  only  in  protected  situa- 
tions (Fig.  2)  or  non-glaciated  areas.  Thus,  for  example,  an  important 
area  of  residual  clay,  derived  from  limestone,  is  found  in  the  driftless 
area  of  Wisconsin.1  This  is  a  silty  clay  in  its  upper  part,  and  a  tough 
jointed  clay  below,  while  scattered  through  it  are  numerous  cherty 
fragments. 

A  second  type  of  residual  clay  occurring  in  Wisconsin  is  that  found 
underlying  the  Potsdam  sandstone  and  has  been  derived  from  the  pre- 
Cambrian  crystallines.  It  represents  probably  the  geologically  oldest 
residual  clay  found  in  the  United  States. 

The  general  character  of  these  residuals  is  much  the  same  whatever 
the  parent  rock.  Nearly  all  are  ferruginous-,  and  contain  angular  mineral 
particles,  as  well  as  more  or  less  decomposed  ones,  from  which  the  more 
soluble  constituents  have  been  leached  out.  The  colors  range  usually 
from  brown  or  red  to  yellow.  In  the  Piedmont  and  Appalachian  areas 

*~Chamberlin  and  Salisbury,  6th  Ann.  Rep.  U.  S.  Geol.  Surv.,  p.  240,  1885. 


ORIGIN   OF  CLAY 


13 


of  the  Southern  States  they  often  attain  great  thickness  and  are  widely 
used  for  brickmaking.1    In  rare  cases  they  are  formed  from  rocks  run- 


FIG.  2. — Generalized  section  showing  three  possible  occurrences  of  kaolin  in  a 
glaciated  country.  1,  limestone;  2,  mica  schist;  3,  pegmatite;  4,  feldspathic 
quartzite;  5,  dark  gneiss;  6,  light  granite;  7,  dark  granite;  8,  kaolin,  pro- 
tected from  glacial  erosion.  Arrow  indicates  direction  of  ice-movement. 
(After  Laughlin,  Conn.  Geol.  and  Nat.  Hist.  Surv.,  Bull.  4,  p.  70,  1905.) 

ning  low  in  iron,  such  as  pegmatite  veins,  and  then  the  clay  is  whitish 
in  color. 

The  following  analyses  2  represent  the  composition  of  several  residual 
clays : 

ANALYSES  OF  RESIDUAL   CLAYS 


Constituents 

I. 

II. 

III. 

IV. 

V. 

VI. 

VII. 

VIIL 

IX. 

X 

SiO2  

71.13 

49.90 

53.09 

49.13 

55,42 

40.127 

39.55 

66.27 

77.24 

55  39 

A1203  ...... 

12.50 

18.64 

21.43 

20.08 

22.17 

13.75 

28.76 

15.25 

26.17 

20  16 

FeoO3  ..... 
FeO  

5.52 
.45 

17.19 
.27 

8.53 
.86 

11.04 
.93 

j-    8.30 

12.315 

16  80 

6.97 

7  76 

8  79 

TiO2  

.45 

.28 

.16 

.13 



.64 

P205  

.02 

.03 

.03 

.04 

.626 

.10 

"  .07 

'".14 

'".04 

MnO  

.04 

,01 

.03 

.06 

CaO  

.85 

.93 

.95 

1.22 

".15 

3.  sis 

'.37 

'".24 

".*iB 

.51 

MgO  

38 

.73 

1.43 

1.92 

1.45 

.479 

.59 

43 

.38 

1  27 

Na2O  ....    . 

2.19 

.80 

1.45 

1.33 

.17 

.006 

tr. 

.40 

.29 

79 

K2O  

1.61 

.93 

.83 

1.60 

2.32 

.118 

tr. 

.86 

4.41 

4  03 

H2O  

*4.63 

*10  46 

*10.79 

*11.72 

*9.86 

t27.441 

13.26 

8.2 

7.38 

C02  

.43 

.30 

.29 

.39 

2.251 

C  

.19 

.34 

.22 

1  09 

100.39 

100  50 

109  09 

100.68 

99  84 

100.631 

100.07 

98.69 

99.27 

98.30 

*  Contains  hydrogen  and  organic  matter.     Dried  at  100°  C. 
t  Contains  11.21  per  cent  of  organic  matter. 

Nos.  I,  II,  III,  and  IV  are  limestone  residuals  from  southern  Wiscon- 
sin. Nos.  I  and  II  are  from  the  same  vertical  section,  I  being  4J  feet 
from  the  surface,  and  II  8J,  and  in  contact  with  the  underlying  lime- 

1  G.  P.  Merrill,  Rocks,  Rock-weathering,  and  Soils,  p.  301;   I.  C.  Russell,  U.  S... 
Geol.  Surv.,  Bull.  52,  1884-85;  H.  Ries;  U.  S.  Geol.  Surv.,  Prof.  Pap.  11. 

2  G.  P.  Merrill,  Rocks,  Rock-weathering,  and  Soils,  p.  306. 


14 


CLAYS 


stone.  Nos.  Ill  and  IV  are  similarly  related,  III  being  3  feet  from  .the 
surface,  and  IV  4^  feet,  the  lower  sample  lying  on  the  unchanged  rock. 
"The  larger  percentages  of  silica,  in  samples  from  nearest  surface,  are 
due  to  higher  state  of  decomposition,  the  soluble  portions  having  been 
more  largely  removed.  The  presence  of  larger  percentages  of  alkalies 
in  these  same  samples  indicates  that  these  salts  existed  in  the  form  of 
silicates  which  have  resisted  the  decomposing  influences,  and  remain 
mechanically  included  in  the  residues/'  No.  V  represents  a  residual  from 
the  Knox  dolomite  at  Morristown,  Ala.;  VI  is  a  red  earth  formed  by  decay 
of  Bermuda  coralline  limestone;  VII  is  a  diabase  residual  from  Wades- 
boro,  N.  C.;  VIII  a  gabbro  subsoil  from  Maryland;  IX  a  Trenton  lime- 
stone residual  from  Hagerstown,  Md.;  and  X  a  Triassic  limestone  residual. 
The  texture  of  some  of  the  above  residual  soils  has  been  determined 
as  follows  1 : 

MECHANICAL  ANALYSES  or  RESIDUAL  CLAYS 


Diameter  of 
particles, 
mm. 

Name. 

I. 

II. 

III. 

IV. 

V. 

2-1 

Fine  gravel  . 

54 

17 

00 

00 

19 

1-   5 

Coarse  sand 

.32 

.00 

.23 

26 

1  80 

5-25 

Medium  sand  

.72 

.15 

1.29 

.18 

3  12 

25-1 

Fine  sand  

.62 

.25 

4.03 

.66 

6  96 

.1     -.05 
05  -  01 

Very  fine  sand  
Silt  

4.03 
36.02 

2.34 
19.04 

11.57 
38.97 

6.73 
47.32 

8.76 
34  92 

01  -  005 

Fine  silt  

14.99 

20.88 

8.84 

10.04 

12  14 

005-  0001 

Clay  . 

41.24 

51.77 

32.70 

34.90 

28  82 

Total  mineral  matter 
Org.   matter,  water, 
loss 

88.48 
1  52 

94.60 
5  40 

97.63 
2  37 

94.44 
5  56 

96.71 
3  29 

100. 

100. 

100. 

100. 

100. 

TRANSPORTED  CLAYS 
Sedimentary  clays 

Origin. — As  mentioned  above,  residual  clays  rarely  remain  on  steep 
slopes,  but  are  washed  away  by  rain-storms  into  streams  and  carried  off 
by  these  to  lower  and  sometimes  distant  areas.  By  this  means  residual 
clays  possibly  of  different  character  may  be  washed  down  into  the  same 
stream  and  become  mixed  together.  This  process  of  wash  and  trans- 
portation can  be  seen  in  any  abandoned  clay  bank,  where  the  clay  of  the 
slopes  is  washed  down  and  spread  out  over  the  bottom  of  the  pit. 

1  M.  Whitney,  Maryland  Agricult.  Exper.  Sta.,  Bull.  21,  1893. 


PLATE  11 


FIG.  1. — Section  showing  beds  of  stratified  clay  overlain  by  glacial  drift. 
(After  Ries,  N.  J.  Geol.  Surv.,  Fin.  Kept.,  VI,  p.  440.) 


FIG.  2. — Bank  of  clay  showing  white  sand  on  right,  passing  into  a  black  clay  on 
the  left.     (After  Ries,  N.  J.  Geol.  Surv.,  Fin.  Rept.,  VI,  p.  12,  1904.) 

15 


ORIGIN    OF  CLAY  17 

As  long  as  the  stream  maintains  its  velocity  it  will  carry  the  clay  in 
suspension,  but  if  its  velocity  be  checked,  so  that  the  water  becomes 
quiet  and  free  from  currents,  the  particles  begin  to  settle  on  the  bottom, 
forming  a  clay  layer  of  variable  extent  and  thickness.  This  may  be  added 
to  from  time  to  time,  and  to  such  a  deposit  the  name  of  sedimentary 
clay  is  applied.  All  sedimentary  clays  are  stratified  or  made  up  of  layers, 
this  being  due  to  the  fact  that  one  layer  of  sediment  is  laid  down  on  top 
of  another  (Plate  II,  Fig.  1).  If  there  were  absolutely  no  difference  in 
the  character  of  the  material  deposited,  it  would  form  one  thick  homo- 
.geneous  bed,  but  there  is  usually  more  or  less  variation,  a  layer  of  very 
fine  material  being  laid  down  at  one  time  and  a  layer  of  coarser  material 
on  top  of  it,  or  vice  versa.  These  layers  may  also  vary  in  thickness,  and 
since  there  is  less  cohesion  between  unlike  particles,  the  two  layers  will 
tend  to  separate  along  their  line  of  contact. 

As  the  finer  material  can  only  be  deposited  in  quiet  water,  and  coarse 
material  in  disturbed  waters,  so  from  the  character  of  the  deposit  we 
can  read  much  regarding  the  conditions  under  which  it  was  formed. 
If,  therefore,  in  the  same  bank  alternating  layers  of  sand,  clay,  and 
gravel  are  found,  it  indicates  a  change  from  disturbed  to  quiet  water, 
and  still  later  rapid  currents  over  the  spot  in  which  these  materials  were 
deposited.  The  commonest  evidence  of  current  deposition  is  seen  in  the 
cross-bedded  structure  of  some  sand  beds  where  the  layers  dip  in  many 
different  directions,  due  to  shifting  currents  which  have  deposited  the 
sand  in  inclined  layers.  The  beds  of  thinly  stratified  or  laminated  sands 
and  clays  found  in  many  of  the  Cretaceous  and  Tertiary  deposits  of  the 
coastal  plain  are  another  example  of  rapid  changes  in  the  conditions  of 
deposition. 

Sedimentary  clays  can  be  distinguished  from  residual  clays  chiefly 
by  their  stratification,  and  also  by  the  fact  that  they  commonly  bear 
no  direct  relation  to  the  underlying  rock  on  which  they  may  rest. 

Structural  irregularities  in  sedimentary  clays. — All  sedimentary  clays 
resemble  each  other  in  being  stratified,  but,  aside  from  this,  they  may 
show  marked  irregularities  in  structure. 

Thus,  any  one  bed,  if  followed  from  point  to  point,  may  show  varia- 
tions in  thickness,  pinching  or  narrowing  in  one  place  and  thickening  or 
swelling  in  others,  as  shown  in  Fig.  3. 

In  digging  clay  the  miner  often  finds  streaks  of  sand  extending  through 
the  deposit  and  cutting  through  several  different  layers,  these  having 
been  caused  by  the  filling  of  channels  cut  in  the  clay  deposits  by  streams 
after  the  elevation  of  the  former  to  dry  land.  Occasionally  a  bed  of  clay 
may  be  extensively  worn  away  or  corraded  by  currents  subsequent  to 


18 


CLAYS 


its  deposition,  leaving  its  upper  surface  very  uneven,  and  on  this  an 
entirely  different  kind  of  material  may  be  deposited,  covering  the  earlier 


- — — • Fireclay 


Sandy  clay  //^r-^--  ;—:~^r:.  \-  ' r---  ~;'  ~T-L'. --^-- ••_•  • ,-  - 


Bed  Rock 


FIG.  3. — Generalized  section  showing  how  beds  may  vary  both    horizontally 

and  vertically. 

bed,  and  filling  the  depressions  in  its  surface.  If  the  erosion  has  been 
deep,  adjoining  pits  dug  at  the  same  level  may  find  clay  in  one  case  and 
sand  in  the  other  (Fig.  4).  Such  irregularities  are  known  to  occur  in 
both  clays  and  shales. 


FIG.  4. — Section  showing  uneven  boundary  of  two  clay  beds,  due  to  erosion  of 
one  before  deposition  of  the  other. 

While  in  many  instances  the  changes  in  the  deposit  are  clearly  visible 
to  the  naked  eye,  variations  may  also  occur,  due  to  the  same  cause,  which 
would  only  show  on  burning.  Thus,  for  example,  the  so-called  retort- 
clay,  found  in  the  Woodb ridge  region  of  New  Jersey,  is  similar  in  its  plastic 
qualities  wherever  found,  but  the  shrinkage  of  that  found  in  the  different 
pits  is  not  always  the  same,  because  it  varies  in  fineness  from  place  to 
place.  It  may  also  vary  in  color. 

CLASSIFICATION  OF  SEDIMENTARY   CLAYS 

The  general  character  of  sedimentary  clays  is  more  or  less  influenced 
by  the  locality  and  conditions  of  deposition,  which  enables  us,  there- 
fore, to  divide  them  into  the  following  classes: 


ORIGIN  OF  CLAY  19 

Marine  clays. — This  class  includes  those  sedimentary  clays  deposited 
on  the  ocean  bottom,  where  the  water  is  quiet.  They  have,  therefore, 
been  laid  down  at  some  distance  from  the  shore,  since  nearer  the  land, 
where  the  water  is  shallower  and  disturbed,  only  coarser  materials  can 
be  deposited.  Beds  of  clay  of  this  type  may  be  of  vast  extent  and  great 
thickness,  but  will  naturally  show  some  variation,  horizontally  at  least, 
because  the  different  rivers  flowing  into  the  sea  usually  bring  down 
different  classes  of  material. 

Thus,  one  stream  may  carry  the  wash  from  an  area  of  iron-stained 
clay,  and  another  the  drainage  from  an  area  of  white  or  light-colored 
clay.  As  a  sediment  spread  out  over  the  bottom,  the  areas  of  deposition 
might  overlap,  and  there  would  thus  be  formed  an  intermediate  zone 
made  up  of  a  mixture  of  the  two  sediments.  This  would  show  itself  later 
as  horizontal  transition  from  one  kind  of  clay  to  another.  These  changes 
may  occur  gradually,  or  at  other  times  within  the  distance  of  a  few  feet 
(Plate  II,  Fig.  2). 

The  laminations  produced  by  vertical  changes  are  shown  in  Plato  II, 
^ig.  1. 

The  most  persistent  beds  of  this  class  are  found  in  the  rocks  of  the 
Silurian,  Devonian,  and  Carboniferous  systems,  but  beds  of  considerable 
horizontal  extent  are  at  times  found  in  the  Mesozoic  formations. 

Estuarine  clays. — These  form  a  second  type  of  some  importance  in 
certain  areas.  They  represent  bodies  of  clay  laid  down  in  shallow  arms 
of  the  sea,  and  are  consequently  found  in  areas  that  are  comparatively 
long  and  narrow,  with  the  deposits  showing  a  tendency  towards  basin 
shapes.  If  strong  currents  enter  the  estuary  from  its  upper  end,  the 
settling  of  the  clay  mud  may  be  prevented,  except  in  areas  of  quiet  water 
in  recesses  of  the  bay  shore.  Or,  if  the  estuary  is  supplied  by  one  stream 
at  its  head,  and  this  of  low  velocity,  the  finer  clays  will  be  found  at  a 
point  most  distant  from  the  mouth  of  the  river.  In  such  cases  we  should 
anticipate  an  increase  in  coarseness  of  the  clay  bed  or  series  of  beds  as 
they  are  followed  from  what  was  formerly  the  old  shore  line  up  to  the 
mouth  of  the  former  river  that  brought  down  the  sediment. 

Estuarine  clays  often  show  sandy  laminations,  and  are  not  infre- 
quently associated  with  shore  marshes,  due  to  the  gradual  filling  up  of 
the  estuary  and  the  growth  of  plants  on  the  mud  flats  thus  formed.  The 
clays  of  the  Hackensack  region  of  New  Jersey  and  those  of  the  Hudson 
Valley  of  New  York  are  good  examples  of  estuarine  deposits,  formed 
at  the  close  of  the  glacial  period,  when  the  region  around  the  Palisades 
stood  somewhat  lower  in  respect  to  sea-level  than  at  present.1 

1  Report  on  Glacial  Geology,  N.  J.  Geol.  Survey,  Vol.  V,  p.  196;  and  N.  Y, 
State  Museum,  Bull.  35,  p.  576. 


20  CLAYS 

Swamp  and  lake  clays. — Swamp  and  lake  clays  constitute  a  third 
class  of  deposits,  which  have  been  formed  in  basin-shaped  depressions 
occupied  by  lakes  or  swamps.  They  represent  a  common  type,  of  vari- 
able extent  and  thickness,  but  all  agree  in  being  more  or  less  basin- 
shaped.  They  not  infrequently  show  alternating  beds  of  clay  and  sand, 
the  latter  in  such  thin  laminae  as  to  be  readily  overlooked,  but  causing  the 
clay  layers  to  split  apart  easily.  Many  of  the  lake  clays  are  directly  or 
indirectly  of  glacial  origin,  having  been  laid  down  in  basins  or  hollows 
along  the  margin  of  the  continental  ice-sheet,  or  else  in  valleys  that  have 
been  dammed  up  by  the  accumulation  of  a  mass  of  drift  across  them. 
This  wall  of  drift  serves  to  obstruct  the  drainage  in  the  valley,  thus  giving 
rise  to  a  lake,  in  which  the  clay  has  been  deposited.  Clay  beds  of  this 
type  are  extremely  abundant  in  all  glaciated  regions.  They  are  usually 
surface  deposits,1  often  highly  plastic,  and  more  or  less  impure.  Their 
chief  use  is  for  common  brick  and  earthenware,  and  they  are  rarely  of 
refractory  character. 

Flood-plain  and  terrace  clays. — Many  rivers,  especially  in  broad  val- 
leys, are  bordered  by  a  terrace  or  plain,  there  being  sometimes  two  or 
more,  extending  like  a  series  of  shelves,  or  steps,  up  the  valley  side.  The 
lowest  of  these  is  often  covered  by  the  river  during  periods  of  high  water, 
and  is  consequently  termed  the  flood-plain.  In  such  times  much  clayey 
sediment  is  added  to  the  surface  of  this  flood-terrace,  and  thus  a  flood- 
plain  clay  deposit  may  be  built  up. 

Owing  to  the  fact  that  there  is  usually  some  current  setting  along 
over  the  plain  when  it  is  overflowed,  the  finest  sediments  cannot  settle 
down,  except  in  protected  spots,  and  consequently  most  terrace  clays 
are  rather  sandy,  with  here  and  there  pockets  of  fine,  plastic  clay.  They 
also  frequently  contain  more  or  less  organic  matter.  Along  its  inner 
edge  the  terrace  may  be  covered  by  a  mixture  of  clay,  sand,  and  stones, 
washed  down  from  neighboring  slopes. 

Where  several  terraces  are  found  it  indicates  that  the  stream  was 
formerly  at  the  higher  levels,  and  has  cut  down  its  bed,  each  terrace 
representing  a  former  flood-plain.  Even  alorig  the  same  stream,  however, 
the  clays  of  the  several  terraces  may  vary  widely  in  their  character,  those 
of  one  terrace  being  perhaps  suitable  for  pottery,  and  those  of  the  sec- 
ond being  available  only  for  common  brick  and  tile.  Examples  of  such 
clays  are  to  be  found  in  most  regions. 

Drift  or  bowlder  clays. — In  that  portion  of  the  United  States  formerly 
covered  by  the  continental  ice-sheet  there  are  occasional  deposits  of  clay 
formed  directly  by  the  glacier.  These  are  usually  tough,  dense,  gritty 

1  Not  necessarily  thin. 


PLATE  III 


FIG.  1. — Deposit  of  stony  glacial  clay.     (After  H.  Ries,  N.  3.  Geol.  Surv. 
Fin.  Kept.,  VI,  p.  128.) 


FIG.  2. — Clay  pit  in  Lignitic  Tertiary  formation,  Athens,  Tex.     Shows  gently 
dipping  layers.     (Photo  by  H.  Ries,  1903.) 

21 


ORIGIN   OF  CLAY 


23 


clays,  often  containing  many  stones  (PL  III,  Fig.  1).  The  material 
deposited  by  the  ice  (till)  was  usually  too  stony  and  sandy  to  serve  as 
clay,  although  often  known  as  bowlder  clay.  Locally,  however,  although 
the  ice-transported  material  has  been  largely  ground  to  a  fine  rock  flour, 
the  bowlder  clay  is  plastic  enough  and  not  too  full  of  stones  for  use. 
Such  deposits  are  mostly  of  limited  extent,  impure,  and  of  little  value. 

In  addition  to  this  type  of  clay  formed  directly  by  the  ice,  there  were 
clays  deposited  in  lakes  or  along  flood-plains  by  the  streams  issuing  from 
the  glacier.  These  were  composed  of  material  derived  from  the  ice,  but 
since  they  were  deposited  by  water  they  were  stratified,  and  may  properly 
be  classed  as  lacustrine,  estuarine,  or  flood-plain  clays  of  glacial  age. 
Bowlder  clays,  although  abundantly  distributed,  are  often  too  stony  to 
be  of  much  value  for  the  manufacture  of  clay  products. 

JEolian  clays. — In  many  parts  of  the  West  there  is  found  a  silty,  often 
calcareous  clay,  termed  the  loess.  This,  although  commonly  a  water 
deposit,  may  at  times  have  been  formed  by  wind  action.  It  could  there- 
fore properly  be  classed  as  transported  clay,  and  would  also  show  a  strati- 
fied structure. 

CLASSIFICATION  OF  CLAY  DEPOSITS 

Clays  may  be  classified  according  to  their  origin,  chemical  and  physi- 
cal properties,  or  uses.  To  the  geologist  the  first  is,  perhaps,  the  most 
important,  to  the  technologist  the  second  and  third  are  of  more  interest. 

Several  such  classifications  have  appeared  in  the  United  States  in  the 
last  few  years,  most  of  them  based  primarily  on  genetic  features,  and 
sometimes  secondarily  on  the  properties  of  the  clay.  They  include  the 
following: 


Orton's  classification.1 


High-grade  clays. 
(50  per  cent  or  more  kaolin) 
with  silica. 


Low-grade  clays. 

(10  to  70  per  cent  kaolin  with  no- 
table per  cent  fluxing  elements. 


1.  Kaolin. 

2.  China-clay. 

3.  Porcelain-clay. 

4.  Fire-clay  (hard). 

5.  Fire-clay  (plastic). 
16.  Potter's,  clay. 

1.  Argillaceous  shale — Paving-block. 

2.  Ferruginous  shale — Pressed  brick. 

3.  Siliceous   clays — Sewer-pipe    and 

paving-block. 

4.  Tile-clays. 

5.  Brick-clays. 

6.  Calcareous  shales — Brick. 


Ohio  Geol.  Survey,  VII,  p.  52. 


'24  CLAYS 

Quality  is  made  the  basis  of  division  in  the  above.  Nos.  1,2,  and  4 
of  the  first  group  are  practically  the  same,  and  the  subdivisions  of  group 
2  are  not  always  distinct.  The  term  kaolin  is  used  incorrectly,  kaolinite 
.being  intended  instead. 

Wheeler's  classification.1 

1.  Whiteware  clays. 

Kaolin. 

China-clay. 

Ball-clay. 

2.  Refractory  clays. 

Plastic  fire-clay. 
Flint-clay. 
Refractory  shale. 

3.  Pottery- clays. 

4.  Vitrifying  clays. 

Paving-brick  clay  and  shale. 
Sewer- pipe  clay  and  shale. 
Roofing-tile  clay  and  shale. 

5.  Brick-clays. 

Common-brick  clay  and  shale. 
Terra-cotta  clay  and  shale. 
Drain- tile  clay  and  shale. 

6.  Gumbo  clays — Burnt-ballast  clay. 

7.  Slip-clays. 

The  qualities  or  uses  of  the  materials  are  here  again  employed  as 
bases  for  subdivision. 

Such  a  classification  is  somewhat  unsatisfactory,  for  the  reason  that 
one  kind  of  clay  might  be  used  for  several  purposes. 

Ladd's  classification.2 

Indigenous. 
A.  Kaolins. 

(a)  Superficial  sheets. 
(6)  Pockets, 
(c)   Veins. 

Foreign  or  transported. 
A.  Sedimentary. 

1  Mo.  Geol.  Surv.,  XI,  p.  25,  1897. 

2  Ga.  Geol.  Surv.,  Bull.  6  A,  p.  12,  1898, 


ORIGIN  OF  CLAY  25 

(a)  Marine. 

1.  Pelagic  (deposited  in  deeper  water). 

2.  Littoral  (deposited  near  shore). 

(b)  Lacustrine  (deposited  in  fresh-water  lakes). 

(c)  Stream. 

1.  Flood-plain. 

2.  Delta. 

B.  Meta-sedimentary. 

C.  Residual. 

D.  Unassorted. 

Under  the  Indigenous  are  included  those  clays  formed  by  the  decay 
of  feldspar  and  other  aluminous  silicates  in  place.  The  Foreign  or  trans- 
ported embrace  all  sedimentary  deposits.  The  meta-sedimentary  clays 
are  chemical  products  resulting  from  the  decomposition  of  other  trans- 
ported materials,  such  as  volcanic  tuffs,  pumfce;  etc.  The  residual  clays 
include  the  insoluble  residue  left  by  the  dissolving  of  limestones,  while 
under  unassorted  are  included  the  glacial  ones. 

The  term  kaolin,  as  here  used,  includes  all  residual  clays,  except  those 
derived  from  limestones,  and,  since  it  is  not  restricted  to  white-burning 
•ones,  its  use  is  unfortunate.  Furthermore,  the  placing  of  limestone  re- 
siduals in  a  separate  class  seems  a  rather  fine  distinction.  Delta  clays 
hardly  seem  of  sufficient  importance  to  warrant  being  placed  in  a  separate 
class,  and  are  rare. 

Buckley's  classification.1 
I.  Residual  derived  from 

A.  Granitic  or  Gneissoid  Rocks. 

B.  Basic  igneous  rocks. 

C.  Limestone  or  dolomite. 

D.  Slate  or  shale. 

E.  Sandstone. 
II.  Transported  by 

A.  Gravity  assisted  by  water. 

Deposits  near  the  heads  and  along  the  slopes  of  ravines. 

B.  Ice. 

Deposits  resulting  mainly  from  the  melting  of  the  ice  of 
the  glacial  epoch. 

C.  Water. 

Marine. 

Lacustrine. 

Stream. 

1  Wis.  Geol.  Surv.,-Bull.  Vll,  Pt    I,  p.  14. 


CLAYS 

D.  Wind. 
Loess. 

E.  Orton  Jr.'s  classification.1 

A.  Primary  or  residual  clays. 

I.  Entirely  decomposed  feldspathic  rock. 

Kaolin  or  china  clay. 

II.  Partially  decomposed  feldspathic  rock. 
English  Cornwall  stone. 
Porzellanerde  of  the  Germans. 

B.  Secondary  or  transported  clays. 

1.  Deposited  in  still  water, 
(a)  Fire-clays. 

Highly  refractory. 
Flint  fire-clay. 
Plastic  fire-clay. 
Moderately  refractory. 
No.  2  fire-clay. 
Stoneware-clay. 
Sewer- pipe  clay. 
(6)  Shales. 

Slaty  shales. 
Bituminous  shales. 
Clay  shales. 

II.  Deposited  from  running  water. 
Alluvium. 
Sandy  clay. 
Loam. 

III.  Deposited  by  glacial  action. 

Leached — Whitish  or  red  bowlder  clay. 
Unleached — Blue  bowlder  clay. 

IV.  Deposited  by  winds. 

Loess. 

Grimsley  and  Grout's  classification.2 

I.  Residual  clays. 

1.  Kaolin. 

2.  China-  or  porcelain-clay. 

1  Quoted  by  Beyer  and  Williams,  la.  Geol.  Surv.,  XIV.  p.  40,  1904. 
3  W.  Va.  Geol.  Surv.,  Vol.  Ill,  p.  70.  1906, 


ORIGIN  OF  CLAY  27 

II.  Transported  clays. 

A.  Refractory  (fluxing  impurities  low). 

3.  Flint  fire-clay. 

4.  Plastic  fire-clay. 

B.  Semi-refractory  clay  (fluxing  impurities  medium). 

5.  Paving-brick  clay  and  shale. 

6.  Sewer-pipe  clay  and  shale. 

7.  Roofing- tile  clay  and  shale. 

8.  Stoneware-clay  and  shale. 

C.  Non-refractory  (fluxing  impurities  high). 

9.  Pottery  clay. 

(a)  Ball-clay. 

(b)  Flower-  pot  clay. 

10.  Brick-  and  tile-clay  and  shale. 

(a)  Ornamental  brick-clay  and  shale. 

(b)  Terra -co  tta  clay  and  shale. 

(c)  Ornamental  tile-clay  and  shale. 

(d)  Common-brick  and  tile  clay  and  shale. 

11.  Gumbo  ballast-clay. 

12.  Slip-clay. 

Ries'  classification. — The  following  classification  suggested  by  the 
author  is  an  amplification  of  one  proposed  by  him  some  years  ago  1: 

A.  Residual  clays.     (By  decomposition  of  rocks  in  situ.) 

I.  Kaolins  or  china-clays.     (White-burning.) 

(a)  Veins,  derived  from  pegmatite. 

(b)  Blanket  deposits,  derived  from  extensive  areas  of  igneous 

or  metamorphic  rocks. 

(c)  Pockets  in  limestone,  as  indianaite. 

II.  Red-burning  residuals,  derived  from  different  kinds  of  rocks. 

B.  Colluvial  clays,  representing  deposits  formed  by  wash  from  the  fore- 

going and  of  either  refractory  or  non-refractory  character. 

C.  Transported  clays. 

I.  Deposited  in  water. 

(a)  Marine  clays  or  shales.     Deposits  often  of  great  extent. 
White-burning  clays.     Bpll-clays. 
Fire-clays  or  shales.     Buff  burning. 

Impure  clays  or  shales,      j  £Talcareous- 

(  Non-calcareous. 

1  Md.  Geol.  Surv.,  IV. 


28  CLAYS 

(6)  Lacustrine  clays.     (Deposited  in  lakes  or  swamps.) 
Fire-clays  or  shales. 
Impure  clays  or  shales,  red-burning. 
Calcareous  clays,  usually  of  surface  character. 

(c)  Flood-plain  clays. 

Usually  impure  and  sandy. 

(d)  Estuarine  clays.     (Deposited  in  estuaries.) 

Mostly  impure  and  finely  laminated. 
II.  Glacial  clays,  found  in  the  drift,  and  often  stony. 

May  be  either  red-  or  cream-burning. 
III.  Wind-formed  deposits  (some  loess). 
IV.  Chemical  deposits.     (Some  flint-clays.) 

SECONDARY  CHANGES  IN  CLAY  DEPOSITS 

Changes  often  take  place  in  clays  subsequent  to  their  deposition. 
These  may  be  local  or  wide-spread,  and  in  many  cases  either  greatly  im- 
prove the  deposit  or  render  it  worthless.  The  marked  effect  of  some  of 
these  changes  is  often  well  seen  in  some  clay  beds  of  which  only  a  por- 
tion has  been  altered.  These  secondary  changes  are  of  two  kinds,  viz., 
mechanical  and  chemical. 

MECHANICAL    CHANGES 

Tilting,  folding,  faulting. — In  the  uplifting  of  beds  of  clay  or  shale, 
subsequent  to  their  deposition,  the  amount  of  elevation  is  rarely  the  same 
at  all  points  over  a  large  area,  so  that  the  beds  frequently  show  a  variable 
degree  of  tilting.  If  the  uplift  is  accompanied  by  folding  of  the  rocks, 
the  dip  of  the  beds  may  be  quite  steep.  Thus,  for  example,  the  Cre- 
taceous and  Tertiary  clay-bearing  formations  of  the  Atlantic  and  Gulf 
coastal  plain  show  a  gentle  dip  to  the  southeast  and  south  (PI.  Ill, 
Fig.  2),  while  the  Devonian  shales  of  southern  New  York  dip  to  the  south. 
At  Golden,  Colo.  (PI.  XXIV,  Fig.  2),  the  Cretaceous  fire-clays  often 
have  a  dip  of  as  much  as  90°.  Beds  of  clay  and  shale  sometimes  show 
folds  or  undulations.  In  the  case  of  consolidated,  or  hard  beds  these 
may  be  due  to  lateral  pressure,  caused  by  movements  in  the  earth's  crust, 
while  in  soft  beds  the  cause  is  frequently  local.  Many  clay  deposits  in 
the  Northern  States  show  a  local  folding  caused  by  the  shoving  action 
of  the  ice-sheet  during  the  glacial  period.  Such  folds,  however,  are  of 
minor  account  and  affect  only  a  few  beds. 

Where  beds  of  clay  are  gently  folded  into  arches  (anticlinal  folds) 


ORIGIN  OF  CLAY 


29 


and  troughs  (synclinal  folds)  each  bed  slopes  or  dips  away  from  the  axis 
of  an  anticlinal  fold  and  towards  the  axis  of  a  synclinal  fold,  but  if  fol- 


FIG.  5. — Section  of  folded  beds,  with  crest  worn  away,  exposing  different  layers. 
(After  Ries,  N.  J.  Geol.  Surv.,  Fin.  Rept.,  VI,  p.  18,  1904.) 

lowed  parallel  to  the  axis  it  will  remain  at  the  same  level,  provided  the 
axis  itself  is  horizontal. 

Where  a  bed  is  not  sufficiently  elastic  to  bend  under  pressure  it 
breaks,  and  if,  at  the  same  time,  the  beds  on  opposite  sides  of  the  break 
slip  past  each  other,  faulting  is  said  to  occur.  When  the  breaking  sur- 
face or  fault-plane  is  at  a  low  angle  one  portion  of  the  bed  may  be  thrust 


FIG.  6.— Section  showing  strata  broken   by   parallel   fault-planes.     (After  Ries, 
N.  J.  Geol.  Surv.,  Fin.  Rept.,  VI,  p.  15,  1904.) 

over  the  other  for  some  distance.  In  other  cases  the  displacement  may 
amount  to  but  a  few  inches.  Figs.  6  and  7  represent  sections  in  faulted 
strata,  and  in  these-  it  will  be  noticed  that  every  bed  terminates  abruptly 


30 


CLAYS 


at  the  fault-plane,  its  continuation  on  the  other  side  being  at  a  higher 
or  lower  level.    Displacements  of  this  type  are  somewhat  rare  in  surface 


FIG.  7. — Strata  broken  by  fault-plane  of  low  inclination.     (After  Ries,  N.  J.  Geol. 
Surv.,  Fin.  Kept.,  VI,  p.  15,  1904.) 

clays,  and  if  occurring,  the  throw  is  not  apt  to  exceed  a  few  feet.  In  the 
shales  of  pre-Pleistocene  age  the  amount  of  displacement  is  sometimes 
much  greater. 

Both  tilting  and  folding  exert  an  important  influence  on  the  form  and 
extent  of  the  outcropping  beds.  Where  no  tilting  has  occurred,  that  is, 
where  the  beds  are  flat,  only  one  bed,  the  upper  one  of  the  section,  will 
be  exposed  at  the  surface,  where  the  latter  is  level  (Fig.  8),  and  lower 


FIG.  8. — Section  of  horizontal  strata,  with  only  the  top  one  exposed  at  the  surface. 

beds  will   be .  exposed   only   where   stream-valleys   have  been   carved 
(Fig.  9). 

If  the  beds  are  tilted  (Figs.  10  and  11)  or  folded,  and  the  crests  of  the 
folds  worn  off  (Fig.  5),  then  the  different  beds  will  outcrop  on  the  surface 
as  parallel  bands,  whose  width  of  outcrop  will  decrease  with  an  increase 
in  the  amount  of  dip  (Figs.  10  and  11). 

Erosion. — All  land  areas  are  being  constantly  attacked  by  the  weather. 
ing  agents  (frost,  rain,  etc.).  The  effect  of  this  is  to  disintegrate  the  sur- 


ORIGIN   OF  CLAY 


31 


face  rocks  and  wash  away  the  loose  fragments  and  grains.    This  brings 
about  a  general  sculpturing  of  the  surface,  forming  hills  and  valleys, 


FIG.  9. — Horizontal  beds,  with  several  layers  exposed  by  wearing  down  of  the 
land  surface.    (After  Ries,  N.  J.  Geol.  Surv.,  Fm.  Kept.,  VI,  p.  18,  1904.) 

the  former  representing  those  parts  of  the  rock  formations  which  have 
not  yet  been  worn  away.    The  effect  of  this  is  to  cause  phenomena  or 


FIG.  10. — Section  showing  outcropping  of  tilted  strata. 

conditions  which  may  at  first  sight  appear  puzzling,  but  are  neverthe- 
less quite  simple  when  the  cause  of  them  is  understood. 


FIG.  11.— Section  of  vertical  beds.    The  width  of  outcrop   is  the  same  as  the 
actual  width  of  the  bed.    (See  also  PI.  XXIV,  Fig.  2.) 

Let  us  take,  for  example,  a  section  of  horizontal  clay  beds  which 
originally  covered  an  extensive  area  and  were  interstratified  with  sand 


32 


CLAYS 


beds.  In  Figs.  8  and  12,  beds  1  and  3  may  be  taken  to  represent  the 
clays.  In  Fig.  8  we  have  indicated  the  surface  as  it  originally  was,  and  in 
Fig.  12  the  outline  as  it  appears  after  the  land  has  been  exposed  to  weather- 


FIG.  12. — Horizontal  beds  with  several  layers  exposed  by  wearing  down  of  the 

land  surface. 

ing  and  erosion  for  an  extended  period.  Here  we  see  that  the  upper  bed 
is  left  only  on  the  highest  hills  and  has  been  removed  over  a  large  area, 
while  No.  2  caps  the  smaller  knolls,  and  No.  3  outcrops  in  the  sides  of 


FIG.  13. — Inclined  strata,  showing  rise  of  the  bed  above  sea-level,  when  followed  up 
the  slope  or  dip.     (After  Ries,  N.  J.  Geol.  Surv.,  Fin.  Kept.,  VI,  p.  19,  1904.) 

the  deeper  valleys.    Many  small  areas  of  clay  thus  represent  all  that  is 
left  of  a  formerly  extensive  bed. 

If  the  beds  had  a  uniform  dip,  the  conditions  may  be  as  indicated  in 


FIG.  14.— Outcrops  of  a  clay  bed  on  two  sides  of  a  hill  and  its  probable  extension 
into  the  same.     (After  Ries,  N.  J.  Geol.  Surv.  Fin.  Rept.,  VI.) 

Fig.  13.  Here  bed  1  appears  at  the  summit  of  two  hills,  a  and  6,  but  its 
rise  carries  it,  if  extended,  above  the  summit  of  hill  c,  which  is  capped  by 
bed  2.  If  one  did  not  know  that  the  beds  rose  in  that  direction,  it  might 


ORIGIN   OF  CLAY  33 

be  assumed  that  bed  1  passed  into  bed  2,  because  they  are  at  the  same 
level.  This  dipping  of  the  layers,  or  beds,  sometimes  accounts  for  the 
great  dissimilarity  of  beds  at  the  same  level  in  adjoining  pits. 

Where  a  bed  of  clay  is  found  outcropping  at  the  same  level  on  two 
sides  of  a  hill  it  is  reasonable  to  assume  that  it  probably  extends  from  one 
side  to  the  other,  but  it  is  not  safe  to  predict  it  with  certainty,  for,  as  has 
been  mentioned  above,  clay  beds  may  thin  out  within  a  short  distance. 
Furthermore,  the  overlying  material,  or  overburden,  will  become  thicker 
towards  the  center  or  summit  of  the  hill,  so  that  even  if  present  the  clay 
may  be  economically  unworkable  (Fig.  14). 

CHEMICAL   CHANGES 

Nearly  all  clay  deposits  are  frequently  changed  superficially,  at  least, 
by  the  weather  or  by  percolating  surface-waters.    The  changes  are  chiefly 
chemical  and  can  be  grouped  under  the  following  heads : 
Change  of  color. 
Leaching. 
Softening. 
Consolidation. 

Change  of  color. — Most  clay  outcrops  which  have  been  exposed  to 
the  weather  for  some  time  show  various  tints  of  yellow  or  brown.  This 
coloration,  or  rather  discoloration,  is  due  to  the  oxidation,  or  rusting, 
of  the  iron  oxide  which  the  clay  contains.  This  iron  compound  is  usually 
found  in  the  clay  as  an  original  constituent  of  some  mineral,  and  rusts 
out  as  the  result  of  weathering,  so  that  the  depth  to  which  the  weathering 
has  penetrated  the  material  can  often  be  told  by  the  color.  The  lower 
limit  of  this  is  commonly  not  only  irregular,  but  the  distance  to  which  it 
extends  from  the  surface  depends  on  the  character  of  the  deposits,  sandy 
open  clays  being  affected  to  a  greater  depth  than  dense  ones.  The  dis- 
coloration of  a  clay  due  to  weathering  does  not  always  originate  within 
the  material  itself,  for  in  many  instances,  especially  where  the  clay  is 
open  and  porous,  the  water  seeping  into  the  »clay  may  bring  in  the  iron 
oxide  from  another  layer,  and  distribute  it  irregularly  through  the  lower 
clay. 

The  changes  of  color  noticed  in  clay  are  not  in  every  case  to  be  taken 
as  evidence  of  weathering,  for  in  many  instances  the  difference  in  color 
is  due  to  differences  in  chemical  composition.  Many  clays  are  colored 
black  at  one  point  by  carbonaceous  matter,  whereas  a  short  distance  off 
the  same  bed  may  be  white  or  light  gray,  due  to  a  smaller  quantity  of 
carbonaceous  material.  In  many  of  the  Lower  Cretaceous  clays  of  New 
Jersey,  for  example,  there  is  often  a  change  from  blue  to  red  and  white 


34 


CLAYS 


mottled,  and  from  this  into  red  clay.  This  is  not  the  result  of  weathering, 
but  is  due  to  local  variations  in  the  iron-oxide  contents  of  the  different 
layers. 

Discoloration  caused  by  weathering  can  usually  be  distinguished 
from  differences  in  color  of  a  primary  character  in  that  the  former  begins 
at  the  surface  and  works  its  way  into  the  clay,  penetrating  to  a  greater 


FIG.  15. — Section   showing  how  weathering  penetrates  a  clay  bed,  particularly 
along  roots,  cracks,  and  joint-planes.     (After  Ries.) 


distance  along  planes  of  stratification  or  fissures,  and  even  following 
plant-roots  as  shown  in  Fig.  15. 

Where  the  clay  deposit  outcrops  on  the  top  and  side  of  a  hill  it  does 
not  follow  that,  because  the  whole  cliff  face  is  discolored,  the  weather  will 
have  penetrated  to  this  level  from  the  surface,  but  indicates  simply  that 
the  weathering  is  working  inward  from  all  exposed  surfaces.  The  over- 


'-  ~ — ~_  —— JH— _j-  _.— _  —  ~~  £"_  "Yellow  Clay 


—  —     - — -  - —    -  Blue  Clay 


Blue-Clay — 


FIG.  16. — Section  showing  weathered  (yellow)  clay  where  the  overburden  is  least. 

/does  not  appreciate  the  important  bearing  which  it  may  have  on  the 

I  behavior  of  his  material.    Some  unweathered  clays  crack  badly  in  dry- 

Vjng  or  burning,  but  weathering  seems  to  mellow  and  loosen  them,  as  well 

burden  often  plays  an  important  role  in  the  weathering  of  clay,  for  the 

greater  its  thickness  the  less  will  the  clay  under  it  be  affected.    This  fact 

is  one  which  the  clay-worker  probably  often  overlooks,  and  therefore 


ORIGIN  OF  CLAY  35 

as  to  increase  their  plasticity,  so  that  the  tendency  to  crack  is  sometimes 
either  diminished  or  destroyed.  If  a  clay  which  is  being  worked  shows 
this  tendency,  it  will  be  advisable  to  search  for  some  part  of  the  deposit 
which  is  weathered,  and  if  the  clay  is  covered  by  a  variable  thickness  of 
overburden,  the  most  weathered  part  will  be  found  usually  under  the 
thinnest  stripping,  as  shown  in  Fig.  16. 

Leaching. — More  or  less  surface-water  seeps  into  all  clays,  and  in  some 
cases  drains  off  at  lower  levels.  Such  waters  contain  small  quantities  of 
carbonic  acid  which  readily  dissolves  some  minerals,  most  prominent 
among  them  carbonate  of  lime.  In  some  areas,  therefore,  where  cal- 
careous clays  occur,  it  is  not  uncommon  to  find  that  the  upper  layers  of 
the  deposit  contain  less  lime  carbonate  than  the  lower  ones,  due  to  this 
solvent  action  of  the  percolating  waters,  and  residual  clays  from  lime- 
stone contain  little  or  no  lime  carbonate. 

Softening. — Most  weathering  processes  break  up  the  clay  deposits, 
either  by  disintegration  or  by  leaching  out  some  soluble  constituents 
that  served  as  a  bonding  or  cementing  material,  thus  mellowing  the  out- 
crop, and  many  manufacturers  recognize  the  beneficial  effect  which 
weathering  has  on  their  clay.  They  consequently  sometimes  spread  it 
on  the  ground  after  it  is  mined  and  allow  it  to  slake  for  several  months 
or,  in  some  cases,  several  years.  The  effect  of  this  is  to  disintegrate 
thoroughly  the  clay,  render  it  more  plastic,  and  break  up  many  injurious 
minerals,  such  as  pyrite.  Although  mentioned  under  Chemical  Changes 
it  will  be  seen  that  the  process  of  softening  is  partly  a  physical  one. 

Consolidation. — This  change  is  found  to  have  taken  place  in  a  few 
deposits,  and  is  due  to  the  formation  of  limonite  crusts  in  the  clay.  At 
times  these  may  form  at  a  few  points  in  the  deposit,  or  only  along 
certain  layers,  but  in  other  instances  they  have  originated  in  all  parts 
of  the  mass,  both  along  the  stratification-planes,  as  well  as  in  every  joint 
or  crack.  They  thus  permeate  the  clay  deposit  with  such  a  network  of 
rusty,  sandstone-like  chunks,  nodules,  and  strips  as  to  seriously  interfere 
with  the  digging  of  the  clay,  and  requiring  powerful  machinery  to  break 
up  the  hard  parts. 

Concretions. — In  some  deposits  the  Hmonite  or  siderite  (carbonate 
of  iron)  collects  around  nuclei,1  such  as  pebbles  or  grains  of  sand,  and 
grows  into  more  or  less  symmetrical  ball-like  concretions,  which,  if  large? 
can  be  avoided  or  thrown  out  in  mining.  These  are  most  abundant  in 
the  weathered  portions  of  the  clay  (Fig.  17).  They  are  not  to  be  con- 

1  The  way  in  which  natural  physical  forces  act  to  bring  about  this  segregation 
of  chemical  compounds  of  the  same  kind  is  not  yet  satisfactorily  explained,  although 
it  is  a  common  phenomenon. 


36 


CLAYS 


lused,  however,  with  the  nodules  and  lumps  of  pyrite  that  are  found 
throughout  some  clay  beds,  and  are  of  yellow  color  and  glistening  metal- 
lic lustre.  These  latter,  although  of  secondary  origin,  are  not  necessarily 
due -to  weathering. 

In  many  calcareous  clays  concretions  (PI.  IV,  Fig.  2)  are  specially 
abundant,  being  found  not  uncommonly  along  lines  of  stratification. 
Many  of  the  drift-clays,  though  free  from  lime,  show  concretionary  lumps, 
.and  in  some  deposits  they  have  been  formed  by  the  deposition  of  lime 


FIG.  17. — Section  showing  occurrence  of  concretions  in  certain  layers. 

carbonate  around  tree-roots.    In  this  case  they  would  be  closely  asso- 
ciated with  weathering. 

Formation  of  shale. — Many  sedimentary  clays,  specially  those  of  ma- 
rine origin,  after  their  formation  are  covered  up  by  many  hundred  feet 
of  other  sediments,  due  to  continued  deposition  on  a  sinking  ocean  bot- 
tom. It  will  be  easily  understood  that  the  weight  of  this  great  thickness 
of  overlying  sediment  will  tend  to  consolidate  the  clay  by  pressure,  con- 
verting it  into  a  firm  rock-like  mass,  termed  shale.  That  the  cohesion 
of  the  particles  is  due  mostly  to  pressure  alone  is  evidenced  by  the  fact 
that  grinding  the  shale  and  mixing  it  with  water  will  develop  as  much 
plasticity  as  is  found  in  many  surface  clays.  An  additional  hardening 
has,  however,  taken  place  in  many  shales,  due  to  the  deposition  of  min- 
eral matter  around  the  grains,  as  a  result  of  which  they  become  more 
firmly  bound  together. 

In  regions  where  mountain-making  processes  have  been  active  and 
folding  of  the  rocks  has  taken  place,  heat  and  pressure  have  been  de- 
veloped, and  the  effect  of  this  has  sometimes  been  to  transform  or 
metamorphose  the  shale  into  slate  or  even  mica-schist  (when  the  meta- 
morphism  is  intense),  both  of  which  are  devoid  of  any  plasticity  when 
ground.  The  shales  utilized  for  clay  products  in  different  parts  of  the 


o 


8.S 

^r^ 

T 


ORIGIN  OF  CLAY  39 

country  show  a  wide  variation  in  their  plasticity.  Those  of  the  Carbon- 
iferous, much  used  in  the  Central  States,  are  often  highly  plastic,  while 
the  red  shales  of  the  Triassic  formation  of  New  Jersey  are  in  most  cases 
consolidated  sandy  clay,  but,  with  one  exception,  all  those  examined 
are  of  poor  plasticity  and  very  low  fusibility.  The  Hudson  River  slates, 
found  over  a  large  area  of  New  Jersey,  New  York,  and  Pennsylvania, 
owe  their  low  plasticity  partly  to  a  slight  metamorphism,  and  partly  to 
the  deposition  of  cement  around  the  grains. 


CHAPTER  II 
CHEMICAL  PROPERTIES  OF  CLAY 

MINERALS   IN    CLAY 

THE  complex  mineralogical  character  of  clay  has  been  referred  to 
on  an  earlier  page,  and  a  microscopic  examination  or  chemical  analysis 
of  a  few  impure  clays  will  convince  one  of  this  fact. 

Nevertheless  the  statement  is  often  made  in  print  that  clay  is  a 
hydrated  silicate  of  alumina  of  the  formula  Al203,2Si02+2H20,  con- 
sequently of  definite  chemical  composition  and  with  a  formula  corre- 
sponding to  that  of  the  mineral  kaolinite. 

That  this  explanation  is  clearly  improbable  can  be  seen  by  examin- 
ing any  series  of  clay  analyses,  few  of  which  will  reduce  to  such  a  formula. 

Equally  sweeping  and  incorrect  is  the  statement  that  kaolinite  is 
the  basis  of  all  clays,  and  that  they  are  therefore  to  be  regarded  as  a 
mixture  of  kaolinite  with  other  minerals 

Many  clays  no  doubt  contain  a  variable  amount  of  kaolinite,1  but 
there  are  others,  consisting  almost  entirely  of  silica,  alumina,  and  water, 
which  clearly  do  not  correspond  to  the  formula  of  the  mineral  above 
mentioned  (see  H  alloy  site  and  Pholerite) ,  and  in  impure  clays  it  becomes 
a  matter  of  some  difficulty  to  prove  beyond  a  doubt  whether  the  hydrous 
aluminum  silicate  present  is  kaolinite  or  some  other  mineral.2 
We  may  even  express  reasonable  doubt  regarding  the  necessary  presence 
of  kaolinite  for  the  development  of  plastic  qualities  in  the  mass. 

The  flint-clays  of  Missouri  (many  of  which  correspond  closely  to 
pholerite  in  composition)  when  finely  ground  possess  some  plasticity. 
The  Edwards  County,  Texas,  kaolin  has  even  more  plasticity,  a  tensile 
strength  of  159  Ibs.  per  sq.  in.,  and  an  air  shrinkage  of  6.2,  and  yet  it 

1  Kaolins  of  commerce  and  ball  clays. 

2  This  fact  has  also  been  emphasized  by  G.  P.  Merrill,  Non-metallic  Minerals, 
p.  217  1904. 

40 


CHEMICAL  PROPERTIES  OF  CLAY  41 

dees  not  correspond  exactly  to  the  formula  of  kaolinite,  but  stands 
intermediate  between  halloysite  and  kaolinite. 

Wheeler  has  described  an  halloysite  from  Missouri 1  which  is  slightly 
plastic  even  when  ground  to  pass  20  mesh,  and  has  an  average  tensile 
strength  of  38  Ibs.  per  sq.  in. 

The  number  of  different  minerals  present  in  a  clay  is  often  no  doubt 
large  and  depends  partly  on  the  mineralogical  composition  of  the  rock 
or  rocks  from  which  the  clay  has  been  derived,  and  partly  on  the  extent 
to  which  the  mineral  grains  in  the  clay  have  been  destroyed  by  weather- 
ing; but  in  any  case  the  identification  of  mineral  species  is  rendered 
rather  difficult,  chiefly  because  of  the  extreme  fineness  of  the  grains,  and 
partly  because  these  are  often  surrounded  by  decomposition  products. 

More  attention  has  been  given  to  the  mineralogy  of  soils  than  of  clays, 
but  since  the  former  are  in  many  cases  nothing  more  than  surface  clays, 
what  is  true  of  the  one  is  more  or  less  so  of  the  other. 

Chamberlin  and  Salisbury,2  in  studying  the  residuals  of  the  Wis- 
consin driftless  area,  were  abk  to  identify  such  minerals  as  plagio- 
clase,  orthoclase,  biotite,  muscovite,  hornblende,  augite,  magnetite, 
and  quartz,  while  Ladd,  in  studying  the  Georgia  Cretaceous  clays,3 
has  noted  kaolinite,  feldspar,  quartz,  muscovite,  biotite,  magnetite, 
titanite,  limonite,  calcite,  and  prochlorite.  In  the  Wisconsin  materials 
Buckley  4  records  finding  quartz,  feldspar,  mica,  calcite,  dolomite,  and  iron 
oxide.  The  Leda  clays  of  Canada  5  show  quartz,  orthoclase,  plagioclase. 
mica,  tourmaline,  pyroxene,  chlorite,  and  hornblende. 

In  the  study  of  soils  perhaps  the  largest  number  of  species  have  been 
determined  by  Delage  and  Lagatu,6  who  include  in  their  list  calcite, 
quartz,  biotite,  muscovite,  sericite,  orthoclase,  oligoclase,  zircon,  tour- 
maline, amphibole,  apatite,  andalusite,  titanite,  microcline,  limonite, 
hematite,  chlorite,  augite,  etc. 

The  more  important  of  these  may  be  referred  to  in  more  than  a 
passing  manner. 

1  Mo.  Geol.  Surv.,  XI,  p.  186,  1896. 

2  U.  S.  Geol.  Surv.,  6th  Ann.  Rept.,  245. 

3  Amer.  Geol.,  XXIII,  p.  240,  1899. 

4  Wis.  Geol.  and  Nat.  Hist.  Surv.,  Bull.  VII,  Pt.  I. 

6  Merrill,  Rocks,  Rock-weathering,  and  Soils,  p.  335. 

e  Ann.  de  Pe"cole  nationale  d'agriculture  de  Montpellier,  VI,  pp.  200-220,  1905; 
also  Comptes  rend.,  CXXXIX,  p.  1044,  1904.  See  also  F.  Steinriede,  Anleitung  zur 
mineralogischen  Bodenanalyse,  Halle,  1889;  Dumont,  Comp.  rend.,  CXL,  p.  1111, 
1905;  Tebier,  ibid..,  CVIII,  p.  1071,  1889;  and  Cameron  and  Bell,  Bur.  of  Soils, 
Bull.  30,  p.  11,  1905,  and  Bull.  22,  p.  12,  1903. 


42  CLAYS 


Hydrous  Aluminum  Silicates 

Kaolinite. — This  mineral  is  a  hydrated  silicate  of  alumina,  repre- 
sented by  the  formula  .11203,28102,21120,  which  corresponds  to  a 
composition  of  Silica  (Si02),  46.3  per  cent;  Alumina  (A12O3),  39.8  per 
cent;  Water  (H20),  13.9  per  cent.  It  is  sometimes  referred  to  as  clay 
substance,  and  is  that  portion  of  the  clay  which  is  soluble  in  hot  sul- 
phuric acid  and  sodium  carbonate.  It  is  a  white,  pearly  mineral,  crystal- 
lizing in  the  monoclinic  system,  the  crystals  presenting  the  form  of  small 
hexagonal  plates  (PL  V,  Fig.  1)  with  a  hardness  of  2-2.5  and  a  specific 
gravity  of  2.2-2.6.  It  is  naturally  white  in  color,  and  a  mass  of  it  is 
plastic  when  wet,  but  very  slightly  so. 

According  to  Rosenbusch 1  its  index  of  refraction  is  the  same  as 
that  of  Canada  balsam;  the  double  refraction  is  strong.  A  negative 
bisectrix  emerges  from  the  face,  of  the  plate,  and  the  axial  plane  bisects 
the  acute  prism  angle.  The  optical  behavior  is  therefore  very  similar 
to  that  of  muscovite,  and  it  can  only  be  distinguished  with  certainty 
from  colorless  mica  by  chemical  reaction  to  prove  the  absence  of  alkali; 
its  specific  gravity  cannot  be  used  to  advantage  because  of  the  mica- 
ceous form  of  both  minerals. 

It  has  naturally  been  assumed  by  most  writers  that  kaolinite  was  a 
widely  distributed  mineral  in  clays,  but  when  we  come  to  sift  the  evi- 
dence of  its  presence  comparatively  little  is  to  be  found. 

A  microscopic  examination  even  of  the  white  clays  free  from  im- 
purities rarely  reveals  the  presence  of  the  hexagonal  kaolinite  scales, 
although  the  little  vermiculite-like  bunches  of  plates  of  this  mineral 
may  be  present  (Fig.  26);  but  still  even  these  are  rarely  seen  in  the 
more  impure  clays,  and  the  theory  of  the  universal  presence  of  kaolinite 
in  clay  is  probably  traceable  to  the  fact  that  many  white  clays,  after 
having  the  sand  washed  out,  often  approach  kaolinite  in  composition.2 

The  occurrence  of  kaolinite  in  crystals  has  been  noted  from  the 
National  Belle  mine,  Red  Mountain,  Colo.,3  by  Dick  from  Anglesey,4 
as  well  as  by  several  other  writers.5 

Many  kaolins  show  the  bunches  of  kaolinite  plates  referred  to  above, 

1  Physiography  of  Rock-making  Minerals,  Iddings'  translation,  1889,  p.  320. 

2  H.  Ries,  Ala.  Geol.  Survey,  Bull.  6,  p.  41,  1900. 

3  H.  Reusch,  Jahrb.  f.  Min.,  1887,  II,  p.  70. 

4  A.  Dick,  Min.  Mag.,  1876,  VIII,  p.  15. 

5  Safarik,  Bohm.  Ges.  Wiss.,   16th  Feb.,  1870;   Knop,  Neues  Jahr.  Min.,  etc.. 
1859,  p.  595;   Johnson  and  Blake,  Amer.  Jour.  Sci.,  ii,  XLII,  pp.  351  and  867. 


PLATE  V 


FIG.  1. — Photo-micrograph  of  kaolinite.       (After  Merrill,  Non-metallic  Minerals.)) 


FIG.  2.— Washed  kaolin.     (After  Merrill.) 


43 


PLATE  VI 


Photo-micrograph  of  indianaite,  showing  coarseness  of  grain. 


45 


CHEMICAL  PROPERTIES  OF  CLAY  47 

and  the  separation  of  these  by  grinding  was  said  by  Cook 1  to  increase 
the  plasticity. 

Kaolinite  is  always  of  secondary  origin,  and  although  in  most  cases 
it  has  probably  been  derived  from  feldspar,  its  derivation  from  numerous 
other  minerals  has  been  recorded,  although  unaccompanied  by  proof. 

Thus  Rosier2  states  that  the  formation  of  kaolinite  from  scapolite, 
leucite,  nepheline,  sodalite,  hauyne,  analcite,  topaz,  etc.,  is  chemically 
possible,  but  not  proven. 

The  same  may  be  said  in  part  regarding  the  statements  of  Van  Hise,3 
who  lists  andalusite,  anorthoclase,  biotite,  cyanite,  epidote,  leucite, 
microcline,  nephelite,  orthoclase,  plagioclase,  scapolite,  sillimanite,  soda- 
lite,  topaz,  zoisite,  and  garnet  as  the  primary  mineral.  He  gives  the 
formula  for  the  kaolinization  of  feldspar  as  follows : 

2K  AlSi3O8 + 2H2O  +  CO2  =  H4Al2Si209  +  4SiO2  +  K2C03. 

Van  Hise  calculates  that  the  decrease  in  volume,  supposing  the  freed 
silica  as  quartz,  and  the  potassium  carbonate  dissolved,  is  12.57%. 
If  all  the  silica  were  dissolved  (which  is  unlikely),  then  the  volume  de- 
crease would  be  54.44%. 

Pure  kaolin  is  highly  refractory,  but  a  slight  addition  of  fusible  im- 
purities lowers  its  refractoriness. 

Many  kaolins  contain  very  minute  scales  of  white  mica  which  it 
would  be  difficult  to  distinguish  under  the  microscope  from  kaolinite;  and 
since  white  mica  in  a  very  finely  divided  condition  is  not  unlike  kaolinite 
in  its  plasticity,  as  shown  by  the  experiments  of  Vogt,  its  presence  may 
be  of  no  influence,  unless  there  is  an  appreciable  amount  of  it.  The 
following  quotation  4  exhibits  those  experiments : 

"Mr.  Vogt  considers  that  the  plasticity  which  clays  have  is  chiefly 
due  to  the  hydrated  silicate  of  alumina  or  kaolinite.  Experiments  which 
he  made  show  that  the  kaolinite  is  not  the  only  substance  which  remains 
in  suspension  for  a  long  period.  For  his  trials  he  took  quartz  from 
Limousin,  orthoclase  from  Norway,  and  a  potash  mica.  All  three  were 
ground  very  fine,  and  then  washed  in  a  current  of  slightly  ammoniacal 
water.  The  washed  materials  were  then  allowed  to  stand.  After  24 
hours  each  of  the  liquids  was  as  opalescent  as  if  it  had  washed  clay  in 
suspension.  After  nine  days  the  turbidity  still  remained,  but  was  less 

1  Clays  of  New  Jersey,  N.  J.  Geol.  Surv.,  1878. 
2l.c. 

3  Treatise  on  Metamorphism,  p.  352. 

4  Thonindustrie-Zeitung,  1893,  p.  140;   also  Compt.  rend.,  Acad.  Sci.,  Paris,  CX, 
p.  1199,  1890. 


48  CLAYS 

marked.  At  the  end  of  this  time  the  supernatant  liquid  was  ladled  off 
of  each,  and  a  few  drops  of  hydrochloric  acid  added  to  it.  The  suspended 
materials  coagulated  and  settled,  and  the  precipitate  was  collected, 
dried,  and  weighed.  The  mica  which  had  remained  in  suspension  during 
the  nine  days  was  very  fine;  still  the  particles  glittered  in  the  light. 
The  addition  of  hydrochloric  acid  caused  the  instant  settling  of  the  par- 
ticles, which  was  also  noted  by  the  cessation  of  the  glittering.  The 
settlings  of  mica  from  1  liter  of  water  amounted  to  0.15  gram.  This 
fine-grained  mica  possessed  a  plasticity  almost  equal  to  that  of  the 
kaolin. 

"From  the  decanted  liquid  of  the  feldspar  the  hydrochloric  acid 
brought  down  about  0.4  gram  of  this  mineral  per  liter,  while  of  the 
quartz  only  0.1  gram  of  sediment  was  obtained. 

"A  very  plastic  clay  from  Dreux  was  treated  in  the  same  manner, 
and  after  nine  days  a  precipitate  of  0.56  gram  was  brought  down. 

"From  these  experiments  we  see  that  in  washing  kaolin  it  is  impos- 
sible to  free  it  entirely  from  quartz,  feldspar,  and  mica,  if  they  are  present 
in  a  finely  divided  condition." 

Minerals  related  to  Kaolinite 

These  include  several  species,  all  hydrated  silicates  of  alumina. 
Some  of  these  have  been  found  in  crystals  and  are  very  probably  good 
species,  but  others  are  known  only  in  an  amorphous  condition,  which 
may  tend  to  suggest  some  doubt  as  to  their  validity;  in  fact  Johnson 
and  Blake 1  suggested  that  the  name  kaolinite  should  include  all  the 
associated  species  mentioned  below,  and  that  the  term  kaolin  be  retained 
for  the  "more  or  less  impure  commercial  article,"  but  this  usage  seems 
too  comprehensive,  especially  since  some  of  those  hydrous  aluminum 
silicates  mentioned  below  seem  to  have  a  definite  formula  distinctly 
different  from  that  of  kaolinite  proper.  These  associated  species  to- 
gether with  their  characters  are  given  by  Dana  as  follows : 

Halloysite. — A  massive,  clay-like  or  earthy  mineral  with  a  con- 
choidal  fracture  and  showing  little  or  no  plasticity;  hardness  1-2; 
specific  gravity  2.0-2.20;  luster  somewhat  pearly  to  waxy  or  dull; 
color  white,  grayish,  greenish,  yellowish,  and  reddish;  translucent  to 
opaque,  sometimes  becoming  translucent  or  even  transparent  in  water, 
with  an  increase  of  one  fifth  in  weight.  It  is  a  hydrous  silicate  of  alumina 
like  kaolinite,  but  amorphous  and  containing  more  water;  the  amount 
is  somewhat  uncertain,  but  according  to  Le  Chatelier  the  composition 

1  Amer.  Jour.  Sci.,  ii,  XL1I,  p.  351. 


CHEMICAL  PROPERTIES  OF  CLAY 


49 


^~  . 

is  probably  2H20,Al2O3,2SiO2+aq,  or  silica  43.5%,  alumina  36.9%, 

water  19.6%  =  100.  It  is  not  uncommon  in  the  kaolin  deposits  around 
Valleyhead,  Dekalb  County,  Ala.,1  where  it  occurs  as  veins  in  the  kaolin, 
but  no  analysis  of  the  material  is  available. 

A  deposit  has  been  described  by  Wheeler  2  from  five  miles  southwest 
of  Aurora,  Mo.  The  material  is  a  white  porcelain-like  clay,  which  is  more 
or  less  stained  or  intermixed  with  yellow  clay.  It  is  massive,  compact, 
hard,  and  of  low  plasticity.  It  fuses  completely  at  2600°  F.  and  has  the 
following  composition  : 

ANALYSIS  OF  MISSOURI  HALLOYSITE 
Silica  (SiO2)  ............................................     44.12 

Alumina  (A^OJ  ........................................     37.02 

Ferric  oxide  (Fe2O3)  ..........  ............................  33 

Lime  (CaO)  .....................................  .  .  :  .....  19 

Alkalies  (Na2O,K2O)  .....................................  24 

Water  (H2O)  ................................  ...........      18,48 

Total  ..............................................  100.38 

This  analysis  it  will  be  seen  agrees  closely  with  the  theoretic  com- 
position of  this  mineral  given  above. 

G.  P.  Merrill  3  has  also  noted  its  occurrence  in  small  quantities  asso- 
ciated with  kaolin,  in  narrow  veins  in  the  decomposing  gneissic  rock 
near  Stone  Mountain,  Ga. 

The  following  three  analyses  4  represent  the  composition  of  halloysite 
from  different  localities: 

ANALYSES  OF  HALLOYSITE 


I. 

II. 

III. 

Silica  (SiOJ    

39.30 

40.70 

42.91 

Alumina  (Al2Og)  

38.52 

38.40 

38.40 

Lime  (CaO)  

0.75 

0.60 

0.60 

Magnesia  (MgO)  

0.83 

1.50 

1.5 

Ferric  oxide  (Fe  Og) 

1  42 

Manganese  

0.25 

Water 

19  34 

18  00 

18  00 

100.41 

99.20 

101.41 

I.   Elgin,  Scotland.     II.  Steinbruck,  Styria.     III.  Detroit  Mine,  Mono  Lake.  Calif. 

1  Gibson,  Geol.  Surv.  of  Ala.,  Report  on  Murphrees  Valley,  1893,  p.  121. 

2  Mo.  Geol.  Surv.,  XI,  p.  186,  1896. 

3  Non-metallic  Minerals,  p.  225. 

4  Ibid. 


50 


CLAYS 


The  kaolin  found  near  Leaky,  Edwards  County,  Tex./  appears  to  be 
of  intermediate  composition  between  kaolinite  and  halloysite,  and  may 
be  a  mixture  of  the  two. 

Indianaite. — This  is  a  whitish  residual  clay  found  in  Lawrence  County, 
Ind.  (see  Indiana  clays),  which  is  placed  under  halloysite  by  Dana,2 
and  called  allophane  in  the  Indiana  3  Survey  report. 

The  two  following  analyses  show  its  composition,  No.  I  being  given 
by  Dana,  and  No.  II  by  the  Indiana  Survey: 

ANALYSES  OF  INDIANAITE 


I.* 

II. 

III. 

IV. 

Silica  (SiO,,)  

43  25 

44  75 

43  5 

46  3 

Alumina  (Al2Og)  

39.92 

38.69 

36  9 

39  8 

Ferric  oxide  (Fe,O3)  

.95 

Lime  (CaO)  
Magnesia  (MgO)  

}       .69 

f      .37. 
1       .30 

Potash  (K  O) 

} 

f         12 

Soda  (Na  O) 

\       .59 

1        23 

Water  (H  O) 

15  52 

15  17 

19  6 

13  9 

*  The  moisture  has  been  left  out.  and  the  analysis  recalculated  to  100  per  cent. 

While  the  percentage  of  combined  water  in  this  material  is  higher 
than  in  kaolinite,  and  the  silica  lower,  still  they  approach  no  more  closely 
to  those  given  for  halloysite  than  they  differ  from  similar  constituents 
of  kaolinite,  No.  Ill  representing  the  composition  of  the  former,  and 
No.  IV  of  the  latter,  placed  there  for  purposes  of  comparison. 

Pholerite. — This  term  was  first  applied  by  Guillemin  in  1825  4  to  a 
pure  white  pearly  substance,  occurring  in  the  form  of  small  hexagonal 
scales,  soft  and  friable  to  the  touch,  adherent  to  the  tongue,  and  giving 
a  plastic  mass  with  water.  Similar  occurrences  were  noted  later  by 
J.  L.  Smith  5  in  1859,  by  A.  Knop,6  and  by  L.  L.  Koninck.7 

The  composition  of  pholerite  is:  Silica  (Si02)  39.3,  alumina  (A12O3) 
45,  water  (H20)  15.7,  which  corresponds  to  a  chemical  formula  of 
2Al2O3,3Si03,4H20. 

Dana  8  classes  this  under  kaolinite,  and  gives  halloysite  as  a  separate 

1  See  description  of  Texas  clays. 

2  System  of  Mineralogy,  688,  1892. 

3  Ind.  Geol.  Surv.,  29th  Ann.  Kept. 

4  Ann,  des  Mines,  XI,  p.  489. 

6  Amer.  Jour.  Sci.,  ii,  XI,  p.  58. 

6  Neues  Jahrb.  Min.,  1859;    also  Johnson  and  Blake,  Amer.  Jour.  Sci.,  XLIIL 
p.  361,  1867. 

7  Zeitschr.  f.  Kryst.  u.  Min.,  II,  p.  661. 
8Syst.  Min.,  1893,  p.  685. 


CHEMICAL   PROPERTIES   OF  CLAY  51 

species,  but,  in  view  of  the  fact  that  the  pholerite  has  been  found  in 
crystalline  form  and  the  halloysite  not,  this  hardly  seems  reasonable. 

So  far  as  the  author  is  aware  no  crystallized  pholerite  has  been 
described  from  the  United  States,  but  Wheeler  has  pointed  to  its  probable 
presence  in  some  of  the  Missouri  flint-clays,1  in  which  the  silica-alumina 
ratio  ranged  from  0.94  to  1.15.  Now,  since  this  ratio  in  kaolinite  is  1.16 
and  in  pholerite  0.81,  it  seems  quite  probable  that  in  some  at  least  of  the 
Missouri  clays  there  is  a  mixture  of  kaolinite  and  pholerite  present. 

Cook  in  his  report  on  the  New  Jersey  clays2  gives  32  analyses  in 
which  the  combined  silica  has  been  separated  from  the  sand,  and  of 
these  21  seem  to  indicate  the  presence  of  some  pholerite,  their  silica- 
alumina  ratio  ranging  from  0.94  to  1.15. 

If  this  explanation  is  correct,  then  pholerite  is  no  doubt  present  in 
many  other  fire-clays,  and  perhaps  even  some  kaolins.  The  writer  has 
questioned  whether  the  presence  of  bauxite  with  the  kaolinite  might  not 
give  a  mixture  with  a  high  alumina  percentage  similar  to  that  shown 
by  pholerite. 

Nacrite,  according  to  Johnson  and  Blake,3  is  identical  with  pholerite. 

Rectorite.4 — Monoclinic.  In  leaves  or  plates  resembling  mountain- 
leather;  hardness  less  than  that  of  talc;  feels  soapy;  luster  pearly;  color 
pure  white,  sometimes  stained  red  with  iron  oxide.  Composition :  HAlSiO* 
or  Al2O3,2Si02,H20  =  silica  50.0,  alumina  42.5,  water  7.5. 

Newtonite.5 — Rhombohedral.  In  soft,  compact  masses,  resembling 
kaolinite.  Color  white.  Its  composition  is  H8Al2Si2On  +  water,  or 
Al2O3,2SiO2,5H20  =  silica  38.5,  alumina  32.7,  water  28.8.  Sp.  gr.  2.37. 

Allophane. — Amorphous.  As  incrustations  which  are  usually  thin, 
with  mammillary  surface.  Occasionally  almost  pulverulent.  Fracture 
imperfectly  conchoidal  and  shining  to  earthy.  Very  brittle.  Color 
variable.  Translucent.  Hardness  3.  Sp.  gr.  1.85-1.89.  A  hydrous 
aluminum  silicate,  Al2SiO5+5H2O=  silica  23.8,  alumina  40.5,  water  35.7. 

Other  species  listed  by  Dana  in  the  kaolinite  group  are  cimolite, 
montmorillonite,  pyrophyllite,  colly  rite,  and  schrotterite. 

Le  Chatelier's  Experiments. — H.  Le  Chatelier,6  in  studying  the  action 
of  heat  on  certain  clays,  emphasized  the  fact  that  the  hydrated  aluminum 
silicates,  in  spite  of  their  common  occurrence  and  their  industrial  import- 

1  Mo.  Geol.  Surv.,  XI,  p.  50,  1897. 

2  N.  J.  Geol.  Surv.,  1878. 

3  I.e. 

4  Brackett  and  Williams,  Amer.  Jour.  Sci.,  XLII,  p.  16,  1891. 

5  Ibid. 

8  Compt.  rend.,  CIV,  p.  1443,  1887;  also  Ding,  polyt,  Jour.,  CCLXV,  p.  94,  1887.. 


52  CLAYS 

ance,  are  little  known  as  regards  their  chemical  constitution.  They 
generally  form  mixtures  so  complex  that  analysis  alone  furnishes  no 
precise  data  as  to  their  nature,  and  he  suggests  that  by  studying  the 
temperature  of  dehydration  of  these  bodies,  it  may  be  possible  to  iden- 
tify a  small  number  of  chemical  species,  and  to  distinguish  the  presence 
of  each  of  them  in  different  mixtures.  Le  Chatelier  states  that  if  a  small 
quantity  of  clay  is  rapidly  heated  there  occurs  at  the  moment  of  de- 
hydration a  retardation  in  the  rise  of  temperature,  and  this  point  may 
be  utilized  for  establishing  a  distinction  between  the  various  hydrated 
aluminum  silicates. 

As  a  result  of  his  experiments  he  recognized  the  following  groups: 

1.  Halloysite  (2Si02,Al203,2H20+Aq).     Shows  a  retardation  in  the 
rate  of  rise  of  the  temperature  between  150°  and  200°  C.,  a  second  one 
at  700°  C.,  followed  by  a  sudden  acceleration  at  1000°  C. 

2.  Allophane    (SiO2,Al203+Aq).     Retardation    between    150°    and 
220°  C.,  and  acceleration  at  1000°  C. 

3.  Kaolin  (2SiO2,Al2O3,2H20).    Shows  retardation  towards  770°  C., 
and  a  slight  acceleration  towards  1000°  C. 

4.  Pyrophyllite    (4SiO2,Al2O3,H20).    The   first   distinct   retardation 
occurs  at  700°  C.,  and  a  second,  but  less-evident  one,  at  850°  C. 

5.  Montmorillonite    (4Si02,Al2C)3,H20  +  Aq).      First   retardation   at 
about  200°  C.,  a  second  at  770°  C.,  and  a  third  less-marked  one  at  950°  C. 

Other  Minerals 

Quartz. — This  mineral  whose  formula  is  Si02  is  found  in  at  least 
small  quantities  in  nearly  every  clay,  whether  residual  or  sedimentary, 
but  the  grains  are  rarely  large  enough  to  be  seen  with  the  naked  eye. 
They  are  translucent  or  transparent,  usually  of  angular  form  in  residual 
clays  and  rounded  in  sedimentary  ones,  on  account  of  the  rolling  they 
have  received  while  being  washed  along  the  river  channel  to  the  sea, 
or  dashed  about  by  the  waves  on  the  beach  previous  to  their  deposition 
in  deeper,  quiet  water.  The  quartz  grains  may  be  colorless,  but  are  more 
often  colored  superficially  red  or  yellow  by  iron  oxide.  Nodular  masses 
of  amorphous  silica,  termed  chert  or  flint,  are  found  in  some  clays. 
These  are  not  uncommon  in  many  residual  clays  of  the  Southeastern 
States,  and  quartz  pebbles  are  by  no  means  rare  in  many  sedimentary 
clays  of  Mesozoic  or  Pleistocene  age;  indeed,  most  of  the  sand-grains 
found  in  the  coarse,  gritty  surface  clays  of  sedimentary  character  are 
quartz.  This  mineral  also  forms  most  of  the  hard  pebbles  found  in  the 
:so-called  "feldspar"  beds  of  the  Woodbridge  district  of  New  Jersey.1 
'  Ries  and  Kiimmel,  N.  J.  Geol.  Surv.,  Fin.  Kept.,  VI,  p.  468,  1904. 


CHEMICAL   PROPERTIES   OF  CLAY 


Both  quartz  and  flint  are  highly  refractory,  being  fusible  only  at 
cone  35  of  the  Seger  series  (see  Fusibility,  Chap.  Ill),  but  the  presence 
of  other  minerals  in  the  clay  may  exert  a  fluxing  action  and  cause  the 
quartz  to  soften  at  a  much  lower  temperature. 

The  amount  of  quartz  in  clays  varies  from  under  one  per  cent  in 
some  kaolins  or  fire-clays  to  over  50  or  60  per  cent  in  some  very  sandy 
brick-clays. 

Feldspar. — This  mineral  is  nearly  as  abundant  in  some  clays  as  quartz, 
but,  owing  to  the  ease  with  which  it  decomposes,  the  grains  are  rarely 
as  large. 

When  fresh  and  undecomposed  the  grains  have  a  bright  luster,  and 
split  off  with  flat  surfaces  or  cleavages.  Feldspar  is  slightly  softer  than 
quartz,  and  while  the  latter,  as  already  mentioned,  scratches  glass,  the 
former  will  not. 

There  are  several  species  of  feldspar,  which  vary  somewhat  in  their 
chemical  composition,  and  are  known  by  different  names,  as  shown 
below. 

COMPOSITION  OF   FELDSPARS 


Feldspar  Species. 

Chemical  Composition. 

SiO2. 

A1203. 

K2O 

Na2O. 

CaO. 

Orthoclase  

64.70 
68 
62 
53 
43 

18.40 
20 
24 
30 
37 

16.90 

12 
9 
4 

12 
5 
13 
20 

Albite  

Oligoclase  

La/bra,dorit6 

Anorthito 

The  fusing-point  of  feldspar  is  about  cone  9  (see  Seger  Cones,  under 
Fusibility),  but  the  different  species  vary  somewhat  in  their  melting- 
points.  The  feldspar  grains  may,  however,  begin  to  flux  with  other  in- 
gredients of  the  clay  at  a  much  lower  temperature.  (See  under  Alkalies.) 

Mica. — This  is  one  of  the  few  minerals  in  clay  that  can  be  easily 
detected  with  the  naked  eye,  for  it  occurs  commonly  in  the  form  of  thin, 
scaly  particles  whose  bright,  shining  surface  renders  them  very  con- 
spicuous, even  when  small.  Very  few  clays  are  entirely  free  from  mica, 
even  in  their  washed  condition,  for,  on  account  of  the  light  scaly  char- 
acter of  the  mineral,  it  floats  off  with  the  clay  particles.  Some  clays  are 
highly  micaceous,  but  such  are  rarely  of  much  commercial  value. 

There  are  several  species  of  mica,  all  of  rather  complex  composition, 
but  all  silicates  of  alumina,  with  other  bases.  Two  of  the  commonest 


54  CLAYS 

species  are  the  white  mica  or  muscovite,  H3KAl3(Si04)3  =  (Si 
45.2,  A12O3  38,5,  K20  11.8,  H2O  4.5),  and  the  black  mica  or  biotite 
(H1K)2(Mg,Fe)2(Al,Fe)2(Si04)3.  Of  these  two,  the  muscovite  is  the  most 
abundant  in  clay,  because  it  is  not  readily  attacked  by  the  weathering 
agents.  The  biotite,  on  the  other  hand,  decomposes  much  more  rapidly 
on  account  of  the  iron  oxide  which  it  contains.  Other  species  of  the 
mica  group  are  no  doubt  present  in  some  clays.  The  effect  of  mica  in 
burning  is  mentioned  under  Alkalies. 

»   Lepidolite  occurs  in  some  clays,  as  evidenced  by  the  small  amounts 
of  lithia  which  have  been  occasionally  noted.1 

Iron  Ores. — This  title  includes  a  series  of  iron  compounds  which  are 
sometimes  grouped  under  the  above  heading,  because  they  are  the  same 
ones  that  serve  as  ores  of  iron  when  found  in  sufficiently  concentrated 
form.  The  mineral  species  included  under  this  head  are:  Limonite 
<2Fe2O3,3H2O=Fe2O3  85.5%,  H20  14.5%),  hematite  (Fe203),  magnetite 
(Fe3O4),  siderite  (FeC03=FeO  62.1%,  C02  37.9%). 

Limonite. — This  mineral  occurs  in  clays  in  a  variety  of  forms,  and 
is  often  widely  distributed  in  them,  its  presence  when  in  a  finely  divided 
condition  being  shown  by  the  yellow  or  brown  color  of  the  material. 
When  the  clay  is  uniformly  colored  the  limonite  is  evenly  distributed 
through  it,  sometimes  forming  a  mere  film  on  the  surface  of  the  grains; 
at  other  times  it  is  collected  into  small  rusty  grains,  or  again  forms 
concretionary  masses  of  spherical  or  irregular  shape;  in  still  other  clays 
it  is  found  in  the  form  of  stringers  and  crusts,  extending  through  the  clay 
in  many  directions.  The  concretions  are  often  especially  abundant  in 
some  weathered  clays.  At  times  they  take  the  shape  of  thick-walled 
cylindrical  bodies  which  have  apparently  formed  around  plant-roots. 
The  beds  of  sandstone  found  in  many  of  the  sand  and  gravel  deposits 
associated  with  some  clays  are  caused  by  limonite  cementing  the  sand- 
grains  together. 

Limonite  concretions  can  often  be  removed  by  hand-picking.  If 
left  in  the  clay,  they  cause  fused  blotches  which  are  unsightly  and  some- 
times even  cause  splitting  of  the  ware. 

Limonite  is  most  abundant  in  surface  clays,  especially  those  which 
are  of  sandy  character  or  sufficiently  porous  to  admit  the  oxidizing 
waters  from  the  surface.  It  is  also  found  quite  frequently  in  the  weath- 
ered outcrops  of  many  shales. 

Hematite,  the  oxide  of  iron,  is  of  a  red  color  and  may  be  found  in 
clays,  but  it  changes  readily  to  limonite  on  exposure  to  the  air  and  in 
the  presence  of  moisture. 

1  N.  W.  Lord,  Amer.  Inst.  Min.  Eng.,  Trans,,  XII,  505. 


CHEMICAL  PROPERTIES  OF  CLAY  55 

Magnetite,  the  magnetic  oxide  of  iron,  forms  black  magnetic 
.grains,  and,  while  not  common,  is  sometimes  found  when  the 
material  is  examined  microscopically.  Like  the  hematite,  it  changes 
to  limonite. 

Siderite,  the  carbonate  of  iron,  may  occur  in  clay  in  the  following 
forms:  1.  As  concretionary  masses  known  as  clay-ironstones,  ranging 
in  size  from  a  fraction  of  an  inch  to  several  feet  in  diameter!  They  are 
very  abundant  in  some  Carboniferous  shales,  and  are  often  strung  out  in 
lines  parallel  with  the  stratification  of  the  clay.  If  near  the  surface, 
the  siderite  concretions  often  change  to  limonite.  2.  In  the  form  of 
crystalline  grains,  scattered  through  the  clay  and  rarely  visible  to  the 
naked  eye.  3.  As  a  film  coating  other  minerals  in  the  clay.  This  min- 
eral will  also  change  to  limonite  if  exposed  to  the  weather. 

When  iron  carbonate  is  in  a  finely  divided  condition  and  evenly 
distributed  through  the  clay  it  may  give  it  a  blue  or  slate-gray 
color. 

Siderite  may  be  present  in  some  surface  clays,  but  it  is  probably  of 
greatest  importance  in  shales,  notably  those  associated  with  coal-seams, 
and  may  occur  in  either  finely  divided  (disseminated)  or  concretionary 
form. 

Pyrite  (FeS2=Fe  46.6%,  S  53.4%).— This  mineral,  which  is  not 
uncommon  in  some  clays,  can  be  often  seen  by  the  naked  eye,  and  is 
known  to  the  clay-miners  in  some  districts  as  sulphur.  It  has  a  yellow 
color,  metallic  luster,  and  occurs  in  large  lumps,  small  grains  or  cubes, 
or  again  in  flat  rosette-like  forms.  Not  infrequently  it  is  formed  on  or 
around  lumps  of  lignite,  showing  quite  clearly  that  the  carbonaceous 
matter  has  reduced  some  iron  sulphate  present  to  sulphide.  It  is  a 
familiar  object  to  all  clay-miners  of  the  Raritan  district  of  New  Jersey, 
and  abundant  also  in  many  Carboniferous  clays. 

When  exposed  to  the  weather  pyrite  alters  rather  easily,  first  to  the 
sulphate  of  iron  and  then  to  limonite.  Clays  containing  pyrite  are  not, 
as  a  rule,  desired  by  the  clay-worker,  and  in  mining  the  pyritic  material 
is  rejected. 

Pyrite  may  be  found  in  almost  any  clay  or  shale,  but  owing  to  the 
ease  with  which  it  is  converted  into  limonite  its  formation  or  permanence 
in  surface  clays  is  rare. 

Calcite  (CaC03  =  CaO  56.00%,  C02  44.00  %) .—This  mineral,  when 
abundant,  is  found  chiefly  in  clays  of  recent  geological  age,  but  some 
shales  also  contain  considerable  quantities  of  it.  It  can  be  easily  de- 
tected, for  it  dissolves  rapidly  in  weak  acids,  and  effervesces  violently 
upon  the  application  of  a  drop  of  muriatic  acid  or  even  vinegar.  It  is 


56  CLAYS 

rarely  present  in  grains  large  enough  to  be  seen  with  the  naked  eye,  but 
has  been  detected  with  the  microscope.1 

In  some  clays  calcite,  as  well  as  some  other  minerals,  may  form  con- 
cretions. Many  of  the  lacustrine  and  glacial  clays  found  in  Wisconsin 
and  Michigan  contain  large  quantities  of  lime  carbonate,  and  some  of 
those  found  in  other  states  are  highly  calcareous.  The  flood-plain  clays 
mentioned  under  Texas  often  carry  a  high  percentage  of  carbonate  of 
lime. 

Gypsum  (CaS04,2H20=CaO  32.6%,  S03  46.5%,  H20  20.9%).- 
It  is  doubtful  whether  this  mineral  is  widely  distributed  in  clays,  but  it 
is  true  that  some  deposits  contain  large  quantities  of  it.  It  may  occur 
in  a  finely  divided  condition,  or  in  the  form  of  crystals,  plates,  or  fibrous 
masses  of  selenite. 

The  Salina  shales  of  New  York  frequently  contain  large  plates  of 
nearly  clear  selenite,  while  some  clays  of  the  southern  Atlantic  coastal 
plain  exhibit  fine  crystals  of  it.  Its  softness,  pearly  luster,  and  trans- 
parency render  its  identification  easy  when  the  pieces  are  of  macroscopic 
size.  When  heated  to  a  temperature  of  250°  C.  (482°  F.)  the  gypsum 
loses  its  water  of  combination,  and  when  burned  to  a  still  higher  tem- 
perature the  sulphuric  acid  passes  off. 

Rutile  (Ti02=Ti  60%,  O  40%)  is  presumed  to  be  of  wide-spread 
occurrence  in  clays,  because  titanium  is  usually  found  on  chemical  analy- 
sis when  proper  tests  are  made.  Rutile  grains  can  be  seen  under  the 
microscope  in  many  fire-clays,  and  the  analyses  frequently  show  the 
presence  of  titanium  oxide  to  the  extent  of  two  per  cent  or  more.  The 
presence  of  this  mineral,  however,  is  unfortunately  too  commonly  ignored 
in  the  analysis  of  clay,  and  yet,  as  will  be  shown  later,  its  effect  on  the 
fusibility  of  clay  is  such  that  it  should  not  be  neglected  in  the  higher 
grades  at  least.  It  occurs  mostly  in  the  form  of  bristle-like  crystals. 
No  systematic  study  of  their  occurrence  in  clay  has  ever  been  taken  up. 
The  writer  has  observed  them  in  some  of  the  Staten  Island,  N.  Y.,  clays, 
and  reference  has  been  made  to  them  from  time  to  time  by  other  writers.2 
Hmenite  (TiFe203)  probably  occurs  in  clays,  but  as  far  as  the  writer 
is  aware  its  presence  has  not  been  definitely  mentioned.  If  present,  it 
would  probably  be  in  part  altered  to  leucoxene  Hmenite  is  most  likely 
to  occur  in  those  clays  which  have  been  derived  from  soda-rich  and  basic 
eruptive  rocks. 

1  Wheeler,  Mo.  Geol.  Surv.,  XI;    Buckley,  Wis.  Geol.  and  Nat.  Hist.  Survey, 
Bull.  VII,  Pt.  I. 

2  See  J.  J.  H.  Teall,  Min.  Mag.,  Ill,  201;  G.  E.  Ladd,  Amer.  Geol.,  XXIII,  240, 
1899. 


CHEMICAL   PROPERTIES  OF  CLAY  57 

Glauconite,  a  hydrous  silicate  of  potash  and  iron,  is  a  common 
ingredient  of  some  clays.  Its  composition  is  often  somewhat  variable, 
and  it  may  contain  other  ingredients  as  impurities.  Thus  a  sample 
from  New  Jersey  analyzed:1  Silica  50.70%,  alumina  8.03%,  iron 
oxide  22.50%,  magnesia  2.16%,  lime  1.11%,  potash  5.80%,  soda  0.75%, 
water  8.95%.  It  is  an  easily  fusible  mineral,  and  hence  a  high  percentage 
of  it  is  not  desired  in  a  clay.  It  is  found  in  the  Clay  Marl  formations 
of  the  New  Jersey  Cretaceous,2  and  in  the  Eocene  formations  of  Mary- 
land 3  and  other  coastal-plain  states. 

Dolomite  and  Magnesite.— Dolomite  (CaMgCO3  =  CaO  30.4%,  MgO 
21.7%,C02  47.8%)  and  magnesite  (MgC03  =  MgO  47.6%,C02  52.4%) 
may  both  occur  in  clay.  They  are  soft  minerals  resembling  calcite,  and 
either  alone  is  highly  refractory,  but  when  mixed  with  other  minerals  they 
exert  a  fluxing  action,  although  not  at  so  low  a  temperature  as  lime. 

In  some  residual  clays  derived  from  dolomitic  limestone  the  grains 
of  the  dolomite  are  clearly  visible  in  those  portions  of  the  mass  in  which 
disintegration  has  not  proceeded  very  far. 

Hornblende  and  Garnet. — These  are  both  silicate  minerals  of  com- 
plex composition,  which  are  probably  abundant  in  many  impure  clays, 
but  their  grains  are  rarely  larger  than  microscopic  size.  Both  are  easily 
fusible,  and  weather  readily  on  account  of  the  iron  oxide  in  them,  and 
therefore  impart  a  deep-red  color  to  clays  formed  from  rocks  in  which 
they  are  a  prominent  constituent. 

Garnet  in  fair-sized  grains  has  been  noted  by  the  writer  in  some  of 
the  North  Carolina  kaolins. 

Vanadiates,  though  not  common  in  clays,  may  cause  discoloration. 
In  Germany  they  have  been  found  in  clays  associated  with  the  lignites, 
and  also  in  some  fire-clays,4  but  in  this  country,  so  far  as  the  writer  is 
aware,  they  have  never  been  investigated.  Clays  containing  soluble 
vanadiates,  if  not  burned  at  a  sufficiently  high  temperature,  will  show 
on  the  surfa.ce  of  the  ware  a  green  discoloration  which,  though  it  can  be 
washed  off  with  water,  will  continue  to  return  as  long  as  any  of  the  salt 
is  left  in  the  brick.  Vanadiates  may  be  rendered  insoluble  by  burning 
the  clay  to  a  point  of  vitrification.5 

Tourmaline. — Since  this  mineral  is  not  an  uncommon  constituent  of 
many  pegmatite  veins,  it  is  sometimes  found  in  kaolins  derived  from 
pegmatites.  Large  crystals  of  tourmaline  are  frequently  found  in  the 
kaolin  of  Henry  County,  Virginia. 


1  N.  J.  Geol.  Surv.,  Fin.  Kept.,  VI,  p.  46,  1904.      4  Seger,  Ges.  Schrift,  p.  301. 

2  Ibid.,  p.  151.  5Ibid. 

3  Md.  Geol.  Surv.,  Eocene,  p.  52,  1901. 


58  CLAYS 

Manganese  oxides. — These  occur  in  many  clays  in  small  amounts, 
and  when  determined  are  found  to  rarely  exceed  one  per  cent.  In  some 
residual  clays  the  manganese  has  been  sufficiently  concentrated  to  be 
worth  collecting. 

Vivianite  (Fe2P2O8-f8H2O  =  FeO  43%,  P205  28.3%,  H2O  28.7%)  has 
not  been  described  as  a  common  constituent  of  clay.  It  has  been  noted 
in  certain  Pleistocene  clays  of  Maryland,1  in  which  it  occurs  as  small 
blue  spots.  It  is  not  known  what  effect  large  quantities  of  it  might  have 
on  the  clay. 

Rare  elements. — Even  such  rare  elements  as  cerium,  yttrium,  and 
beryllium  oxides  have  been  determined  in  some  clays.2 

THE    CHEMICAL   ANALYSIS    OF   CLAYS 

There  are  two  methods  of  quantitatively  analyzing  clays.  One  of 
these  is  termed  the  ultimate  analysis,  the  other  is  known  as  the  rational 
analysis. 

The  ultimate  analysis. — In  this  method  of  analysis,  which  is  the  one 
usually  employed,  the  various  ingredients  of  a  clay  are  considered  to 
•exist  as  oxides,  although  they  may  really  be  present  in  much  more  com- 
plex forms.  Thus,  for  example,  calcium  carbonate  (CaCO3),  if  it  were 
present,  is  not  expressed  as  such,  but  instead  it  is  considered  as  broken 
up  into  carbon  dioxide  (C02)  and  lime  (CaO),  with  the  percentage  of 
each  given  separately.  The  sum  of  these  two  percentages  would,  how- 
ever, be  equal  to  the  amount  of  lime  carbonate  present.  While  the 
ultimate  analysis,  therefore,  fails  to  indicate  definitely  what  compounds 
are  present  in  the  clay,  still  there  are  many  facts  to  be  gained  from  it. 
The  ultimate  analysis  of  a  clay  might  be  expressed  as  follows: 

Silica (SiO2) 

Alumina (A12O3) 

Ferric  oxide ....  (Fe2O3) 
Lime (CaO) 


Fluxing  impurities 


Magnesia  .......  (MgO) 


Alkalies.,  j 
( 


Soda  ...........  (Na20) 

Titanic  oxide.  .  .  (TiO2) 
Sulphur  trioxide.(S03) 
Carbon  dioxide.  .  (CO2) 
Water  .........  (H2O) 


1  Md.  Geol.  Surv.,  IV,  228,  1902. 

2  J.  R.  Strohecker,  Jour,  prakt.  Chem.  (2),  XXXIII,  p.  132;  Abs.  Jour.  Chem. 
•Soc.,  L,  p.  314,  1886. 


CHEMICAL  PROPERTIES  OF  CLAY  59 

In  most  analyses  the  first  seven  of  these  and  the  last  one  are  usually 
determined.  The  percentage  of  carbon  dioxide  is  small,  except  in  very 
calcareous  clays,  and  therefore  commonly  remains  undetermined.  Titanic 
oxide  is  rarely  looked  for,  except  in  fire-clays,  and  even  here  its  presence 
is  frequently  neglected.  Since  the  sulphur  trioxide,  carbon  dioxide,  and 
water  are  volatile  at  a  red  heat,  they  are  often  determined  collectively 
and  expressed  as  "loss  on  ignition."  If  carbonaceous  matter,  such  as 
lignite,  is  present,  this  also  will  burn  off  at  redness.  To  separate  these 
four,  special  methods  are  necessary,  but  they  are  rarely  applied,  and 
in  fact  are  not  very  necessary  except  in  calcareous  clays  or  highly  car- 
bonaceous ones.  The  loss  on  ignition  in  the  majority  of  dry  l  clays  is 
chiefly  chemically  combined  water.  The  ferric  oxide,  lime,  magnesia, 
potash,  and  soda  are  termed  the  fluxing  impurities,  and  their  effects  are 
discussed  under  the  head  of  Iron,  Lime,  Magnesia,  etc.,  and  also  under 
Fusibility  in  Chapter  III. 

All  clays  contain  a  small  but  variable  amount  of  moisture  in  their 
pores,  which  can  be  driven  off  at  100°  C.  (212°  F.).  In  order,  therefore, 
to  obtain  results  that  can  be  easily  compared,  it  is  desirable  to  make 
the  analysis  on  a  moisture-free  sample  which  has  been  previously  dried 
in  a  hot-air  bath.  This  is  unfortunately  not  universally  done. 

Interpretation  of  ultimate  analysis. — The  facts  obtainable  from  the 
ultimate  analysis  of  a  clay  are  the  following: 

1.  The  purity  of  the  clay,  showing  the  proportions  of  silica,  alumina, 
combined  water,  and  fluxing  impurities.     High-grade  clays  show  a  per- 
centage of  silica,  alumina,  and  water  approaching  quite  closely  to  those 
of  kaolinite. 

2.  The  refractoriness  of  the  clay;  for,  other  things  being  equal,  the 
greater  the  total  sum  of  fluxing  impurities,  the  more  fusible  the  clay. 

3.  The  color  to  which  the  clay  burns.     This  may  be  judged  approxi- 
mately, for  clays  with  several  per  cent  or  more  of  ferric  oxide  will  burn 
red,  provided  the  iron  is  evenly  and  finely  distributed  in  the  clay,  and 
there  is  no  excess  of  lime  or  alumina.     The  above  conditions  will  be 
affected  by  a  reducing  atmosphere  in  burning,  or  the  presence  of  sul- 
phur in  the  fire  gases.2 

4.  The  quantity  of  water.     Clays  with  a  large  amount  of  chemically 
combined  water  sometimes  exhibit  a  tendency  to  crack  in  burning,  and 
may  also  show  high  shrinkage.     If  a  hydrous  aluminum  silicate  of  a 
composition  closely  resembling  kaolinite  is  the   only  mineral  present 
containing  chemically  combined  water  the  percentage  of  the  latter  will 

1  This  means  dried  at  100°  C.  until  their  weight  is  constant.    See  under  Moisture. 

2  See  Lime  and  Iron  in  this  chapter. 


60 


CLAYS 


be  approximately  one  third  that  of  the  percentage  of  alumina,  but  if 
the  clay  contains  much  limonite  or  hydrous  silica  the  percentage  of 
chemically  combined  water  may  be  much  higher. 

5.  Excess  of  silica.     A  large  excess  of  silica  indicates  a  sandy  clay. 
If  present  in  the  analysis  of  a  fire-clay  it  indicates  only  moderate  refrac- 
toriness. 

6.  The  quantity  of  organic  matter.     If  this  is  determined  separately, 
and  it  is  present  to  the  extent  of  several  per  cent,  it  would  require  slow 
burning  during  the  oxidation  period  if  the  clay  was  dense. 

7.  The  presence  of  several  per  cent  of  both  lime  (CaO)  and  carbon 
dioxide  (CO2)  in  the  clay  indicates  that  it  is  quite  calcareous. 

Variation  in  chemical  composition  of  clays. — The  variation  in  the 
ultimate  composition  of  clays  is  well  brought  out  by  the  following 
analyses : 

ANALYSES  SHOWING  VARIATION  IN  COMPOSITION  OF  CLAYS 


L     !     H. 

III. 

IV 

V, 

VI. 

VII. 

VIII.      IX, 

X. 

SUica  (SiO2)  

46  3 
39  8 

13.9 

45.70 
40.61 
1.39 

.45 
.09 
2.82 

'8.98 
.35 

57.62 
24.00 
1.9 
1.2 

.7 

:! 

•2 

io  5 

2.7 
35 

59.92 
27.56 
1.03 

tr. 
tr. 

j     .64 
'9.70 

*:12 

68.62 
14.98 
4.16 

'i.'48 
1.09 

3.36 

3.55 

2.78 

82.45 
10.92 
1.08 

.  22 
.96 

{::! 

1.00 
2.4 

54.64 
14.62 
5.69 

'o.!6 
2.90 

5.89 

'3:74 
.85 
4.80 

38.07 
9.46 
2.70 

15.84 
8.50 
2.76 

J2.49 
20.46 

90.00 
4.60 
1.44 
.  . 
.10 
.10 
Jtr. 
1  tr. 
.70 
(3  04 

47.92 
14  40 
3  60 
.... 
12.30 
1.08 
1.20 
1  50 
1  22 
4.85- 

'9.50- 
1.44 
1.34 

Ferric  oxide  (Fe2O3)  .  .  . 
Ferrous  oxide  (FeO).  . 
Lime  (CaO)  
Magnesia  (MgO)  
Potash  (K2O) 

Soda  (Na2O)  
Titanic  oxide  (TiO2).  . 
Water  (H2O)  
Moisture  
Carbon  dioxide  (CO2).  .. 
Sulphur  trioxide  (SO3). 
Organic  matter  
Manganous  oxide  (  MnO) 

.64 

".'76 

Total  100.00  100.39J100.07 

99.97 

100.66 

99  .  03 

99.06 

100.  2S 

99.  98;  100.  35- 

I.  Kaolinite. 
II.  Kaolin,  Webster,  N.  Ca. 

III.  Plastic  fire-clay,  St.  Louis,  Mo. 

IV,  Flint  fire-clay,  Salines ville,  O. 
V.  Loess-clay,  Guthrie  Centre,  la. 


VI.  Rusk,  Cherokee  County,  Tex. 
VII.  Brick  shale,  Mason  City,  la. 
VIII.  Calcareous  clay,  Milwaukee,  Wis. 

IX.  Sandy  brick-clay,  Colmesneil,  Tex. 

X.  Blue  shale-clay,  Ferris,  Tex. 


Variations  in  the  same  deposit. — Similar  differences  may  not  infre- 
quently be  shown  by  the  different  layers  of  any  one  bank,  as  the  follow- 
ing analyses  indicate: 

ANALYSES  SHOWING  VARIATIONS  IN  THE  SAME  DEPOSIT 


59.' 10 

28.84 


Silica  (SiO2) 

Alumina  (A12O3) ^o .  «•* 

Ferric  oxide  (Fe2O3) 1 . 00 

Lime  (CaO) 

Magnesia  (MgO) 

Potash  (K.,O). 

Soda  (Na2O) 

Titanium  oxide  (TiO.,) 

Water  (H2O) 


.70 
none 
trace 
trace 

.87 
9.30 

99.81 


98.6 


99.8, 


CHEMICAL   PROPERTIES  OF  CLAY  61 

Rational  analysis.1 — This  method  has  for  its  object  the  determination 
of  the  percentage  of  the  different  mineral  compounds  present,  such  as 
quartz,  feldspar,  kaolinite,  etc.,  and  gives  us  a  much  better  conception 
of  the  true  character  of  the  material.  Most  kaolins  and  other  high-grade 
clays  consist  chiefly  of  kaolinite  (or  some  similar  hydrous  aluminum 
silicate),  quartz,  and  feldspar,  the  first  forming  most  of  the  finest  par- 
ticles of  the  mass,  while  the  balance  is  quartz,  feldspar,  and  perhaps 
some  mica.  The  finest  particles  are  known  as  the  clay  substance,  which 
may  be  looked  upon  as  having  the  properties  of  kaolinite.  Now,  as  each 
of  these  three  compounds  of  the  kaolin — clay  substance,  quartz,  and 
feldspar — have  characteristic  properties,  the  kaolin  will  vary  in  its 
behavior  according  as  one  or  the  other  of  these  constituents  predominates 
or  tends  to  increase. 

As  to  the  characters  of  the  three,  quartz  is  of  high  refractoriness 
and  practically  non-plastic,  has  very  little  shrinkage,  and  is  of  low  tensile 
strength;  feldspar  is  easily  fusible,  and  alone  has  little  plasticity;  kao- 
linite is  plastic  and  quite  refractory,  but  shrinks  considerably  in  burning. 
The  mica,  if  extremely  fine,  may  serve  as  a  flux,  and  even  alone  is  not 
refractory.  It  is  less  plastic  than  the  kaolinite,  and,  when  the  percentage 
of  it  does  not  exceed  1  or  2  per  cent,  it  can  be  neglected.  To  illustrate 
the  value  of  a  rational  analysis  we  can  take  the  following  example: 
Porcelain  is  made-  from  a  mixture  of  clay,  quartz,  and  feldspar.  Sup- 
pose that  a  manufacturer  of  porcelain  is  using  a  clay  of  the  following 
rational  composition: 

Clay  substance 67. 82% 

Quartz 30 . 93 

Feldspar 1 .25 

If  now  to  100  parts  of  this  there  are  added  50  parts  of  feldspar,  it 
would  give  a  mixture  whose  composition  is: 

Clay  substance 45 . 21% 

Quartz 20.62 

Feldspar 34. 17 

If,  however,  it  became  necessary  to  substitute  for  the  one  in  use  a 
new  clay  which  had  a  composition  of: 

Clay  substance 66.33% 

Quartz 15.61 

Feldspar 18.91 

1  The  method  is  described  in  the  Manual  of  Ceramic  Calculations,  issued  by  the 
American  Ceramic  Society.  See  also  Langenbeck,  Chemistry  of  Pottery,  1895, 

p.  8. 


62  CLAYS 

and  added  the  same  quantity  of  it  as  we  did  of  the  old  clay,  it  would 
change  the  rational  analysis  of  the  body  to  the  following  proportions: 

Clay  substance 44 . 22% 

Quartz 10.41 

Feldspar 45 . 98 

Such  an  increase  of  feldspar,  as  shown  by  this  formula,  would  greatly 
increase  the  fusibility  and  shrinkage  of  the  mixture;  but,  knowing  the 
rational  composition  of  the  new  clay,  it  would  be  easy,  by  making  a 
simple  calculation,  to  ascertain  how  much  quartz  and  feldspar  should  be 
added  to  bring  the  mixture  back  to  its  normal  composition. 

The  rational  composition  of  a  clay  can  be  determined  from  an  ulti- 
mate analysis,  but  the  process  of  analysis  and  calculation  becomes  much 
more  complex.  The  rational  analysis  is,  furthermore,  useful  only  in 
connection  with  mixtures  of  the  better  grades  of  clay,  in  which  the  varia- 
tion of  the  ingredients  can  only  be  within  comparatively  narrow  limits. 
For  ordinary  purposes  the  ultimate  analysis  is  of  greater  value. 

Comparison  of  ultimate  and  rational  analyses.1 — If  we  compare  the 
ultimate  and  rational  analyses  of  a  series  of  clays  we  find  that  two  clays 
which  agree  closely  in  their  ultimate  composition  may  differ  markedly 
in  their  rational  composition  and  vice  versa,  as  shown  in  the  table  on 
page  63. 

In  this  table  Nos.  I  and  II  represent  two  clays  which  agree  very 
closely  in.  their  ultimate  composition,  but  their  rational  analyses  differ 
by  6  per  cent  in  their  clay  substance,  12  per  cent  in  quartz,  and  nearly 
19  per  cent  in  feldspar.  Nos.  Ill  and  V,  and  X  and  XII  also  illustrate 
this  point. 

In  Nos.  VI  and  VII,  one  a  German  and  the  other  a  North  Carolina 
kaolin,  the  ultimate  analyses  are  very  closely  alike,  and  the  rational 
analyses  also  agree  very  well.  This  is  frequently  the  case  when  the  clay 
substance  is  very  high,  between  96  and  100  per  cent,  as  in  Nos.  IX 
and  XL 

A  third  case  would  be  presented  if  the  rationals  agreed  but  the  ulti- 
mates  did  not,  but  such  instances  seem  to  be  much  less  common. 

1  Ries,  Amer.  Inst.  Min.  Eng.,  Trans.,  XXVIII,  p.  160,  1899. 


CHEMICAL  PROPERTIES  OF   CLAY 


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64  CLAYS 

Method  of  making  Ultimate  Analysis 

The  method  employed  in  making  the  ultimate  analysis  is  usually 
that  outlined  below. 

Moisture. — Two  grams  are  heated  in  a  platinum  crucible  at  100°  C. 
until  they  show  a  constant  weight.  The  loss  is  reported  as  moisture. 

Loss  on  ignition  (combined  water,  and  sometimes  organic  matter, 
etc.) . — The  crucible  and  clay  are  heated  with  a  blast-lamp  until  there  is 
no  further  loss  in  weight. 

Alkalies. — This  same  portion  of  clay,  which  has  been  used  for  deter- 
mining moisture  and  loss,  is  treated  with  concentrated  sulphuric  and 
hydrofluoric  acids  until  it  is  completely  decomposed.  The  acids  are 
evaporated  off  by  heating  upon  the  sand-bath.  The  cooled  crucible  is 
washed  out  with  boiling  water  to  which  several  drops  of  hydrochloric 
acid  have  been  added.  The  solution  after  being  made  up  to  about  five 
hundred  cubic  centimeters  is  boiled,  one-half  gram  ammonium  oxalate 
added,  and  made  alkaline  with  ammonium  hydroxide;  the  boiling  is 
continued  until  but  a  faint  odor  of  ammonia  remains.  The  precipitate 
is  allowed  to  settle  and  is  separated  from  the  liquid  by  filtering  and 
washed  three  times  with  boiling  water.  The  filtrate  is  evaporated  to 
dryness  and  ignited  to  drive  off  ammonium  salts.  The  residue  is  treated 
with  five  cubic  centimeters  of  boiling  water,  two  or  three  cubic  centi- 
meters of  saturated  ammonium  carbonate  solution  are  added,  and  the 
whole  is  filtered  into  a  weighed  crucible  or  dish.  The  precipitate  is 
washed  three  or  four  times  with  boiling  water  and  the  filtrate  evaporated 
to  dryness.  Five  drops  of  sulphuric  acid  are  added  to  the  residue,  and 
then  the  crucible  or  dish  is  brought  to  a  red  heat,  cooled  in  a  desiccator, 
and  the  alkalies  are  weighed  as  sulphates. 

To  separate  the  alkalies,  the  sulphates  are  dissolved  in  hot  water, 
acidified  with  hydrochloric  acid,  sufficient  platinum  chloride  added  to 
convert  both  the  sodium  and  potassium  salts  into  double  chlorides;  the 
liquid  is  evaporated  to  a  syrup  upon  a  water-bath,  eighty  per  cent  alco- 
hol added,  and  filtered  through  a  Gooch  crucible  or  upon  a  tared  filter- 
paper.  The  precipitate  is  thoroughly  washed  with  eighty  per  cent 
alcohol,  dried  at  100°  C.,and  weighed;  the  potassium  oxide  is  calculated 
from  the  double  chloride  of  potassium  and  platinum. 

When  magnesium  was  present  to  as  much  as  one  half  of  one  per  cent 
the  magnesium  hydroxide  was  precipitated  with  barium  hydroxide 
solution,  and  the  barium  in  turn  removed  by  ammonium  carbonate. 
When  the  amount  of  magnesium  was  less  than  the  amount  named,  this 
portion  of  the  ordinary  process  was  not  regarded  as  necessary. 


CHEMICAL  PROPERTIES  OF  CLAY  65 

Silica. — Two  grams  of  clay  are  mixed  with  ten  grams  of  sodium  car- 
bonate and  one-half  gram  of  potassium  nitrate  and  brought  to  a  calm 
fusion  in  a  platinum  crucible  over  the  blast-lamp.  The  melt  removed 
from  the  crucible  is  treated  with  an  excess  of  hydrochloric  acid  and 
evaporated  in  a  casserole  to  dry  ness  upon  a  water-bath,  and  heated  in 
an  air-bath  at  110°  C.  until  all  the  hydrochloric  acid  is  driven  off.  Di- 
lute hydrochloric  acid  is  added  to  the  casserole  now,  and  the  solution 
brought  to  boiling  and  rapidly  filtered.  The  silica  is  washed  thoroughly 
with  boiling  water  and  then  ignited  in  a  platinum  crucible,  weighed,  and 
moistened  with  concentrated  sulphuric  acid.  Hydrofluoric  acid  is  cau- 
tiously added  until  all  the  silica  has  disappeared.  The  solution  is  evap- 
orated to  dryness  upon  a  sand-bath,  ignited,  and  weighed.  The  differ- 
ence in  weight  is  silica.  The  residue  may  contain  iron,  alumina,  and 
titanium. 

Iron  Sesquioxide. — The  filtrate  from  the  silica  is  divided  into  equal 
portions.  To  one  portion  in  a  reducing-flask  are  added  metallic  zinc  and 
sulphuric  acid.  After  reduction  and  filtration  to  free  the  liquid  from 
undissolved  zinc  and  carbon,  the  iron  is  determined  by  titration  with 
a  standard  solution  of  potassium  permanganate. 

Aluminum  Oxide. — To  the  second  portion,  which  must  be  brought 
to  boiling,  ammonium  hydroxide  is  added  in  slight  excess,  the  boiling 
continued  from  two  to  five  minutes,  the  precipitate  allowed  to  settle 
and  then  caught  upon  the  filter,  all  the  chlorides  being  washed  out  with 
boiling  water.  The  precipitate  is  ignited  and  weighed  as  a  mixture  of 
aluminium  oxide  and  iron  sesquioxide.  The  amount  of  iron  sesquioxide 
already  found  is  taken  from  this  and  the  remainder  reported  as 
alumina. 

Calcium  Oxide. — The  filtrate  from  the  precipitate  of  iron  and  alumin- 
ium hydroxides  is  concentrated  to  about  two  hundred  cubic  centimeters, 
and  the  calcium  precipitated  in  a  hot  solution  by  adding  one  gram  of 
ammonium  oxalate.  The  precipitate  is  allowed  to  settle  during  twelve 
hours,  filtered,  and  washed  with  hot  water,  ignited,  and  weighed  as  cal- 
cium oxide.  When  the  calcium  is  present  in  no  table, amounts,  the  oxide 
is  converted  into  the  sulphate  and  weighed  as  such. 

Magnesium  Oxide. — The  filtrate  from  the  calcium  oxalate  precipitate 
is  concentrated  to  about  one  hundred  cubic  centimeters,  cooled,  and  the 
magnesium  precipitated  by  means  of  hydrogen  disodium  phosphate  in 
a  strongly  alkaline  hydroxide  solution.  The  magnesium  ammonium 
phosphate,  after  standing  overnight,  is  caught  upon  an  ashless  filter, 
washed  with  water  containing  at  least  five  per  cent  ammonium  hydroxide, 
burned,  and  weighed  as  magnesium  pyrophosphate. 


66  CLAYS 

Titanic  Oxide. — One-half  gram  clay  is  fused  with  five  grams  potas- 
sium bisulphate  and  one  gram  sodium  fluoride  in  a  spacious  platinum 
crucible.  The  melt  is  dissolved  in  five  per  cent  sulphuric  acid.  Hydro- 
gen dioxide  is  added  to  an  aliquot  part  and  the  tint  compared  with  that 
obtained  from  a  standard  solution  of  titanium  sulphate. 

A  simpler  plan  is  to  fuse  the  ignited  alumina  and  iron  oxides  with 
potassium  bisulphate,  dissolve  this  in  warm  water,  a  little  sulphuric  acid, 
and  then  titrate  with  permanganate  for  ferric  oxide.  This  same  solu- 
tion can,  after  the  disappearance  of  the  permanganate  color,  be  treated 
with  hydrogen  peroxide  as  outlined  above. 

Sulphur  (total  present). — The  sulphur  is  determined  by  fusing  one- 
half  gram  of  clay  with  a  mixture  of  sodium  carbonate,  five  parts,  and 
potassium  nitrate,  one  part.  The  melt  is  brought  into  solution  with 
hydrochloric  acid.  The  silica  is  separated  by  evaporation,  heating,  re- 
solution, and  subsequent  filtration.  Hydrochloric  acid  is  added  to  the 
filtrate  to  at  least  five  per  cent,  and  the  sulphuric  acid  is  precipitated 
by  adding  barium  chloride  in  sufficient  excess,  all  solutions  being  boil- 
ing hot.  The  barium  sulphate  is  filtered  off  and  washed  with  hot  water, 
burned,  and  weighed  as  such. 

Ferrous  Oxide  is  determined  by  fusing  one-half  gram  with  five  grams 
sodium  carbonate,  the  clay  being  well  covered  with  the  carbonate,  the 
top  being  upon  the  crucible.  The  melt  is  dissolved  in  a  mixture  of  di- 
lute hydrochloric  and  sulphuric  acids  in  an  atmosphere  of  carbon  dioxide. 
The  ferrous  iron  is  determined  at  once  by  titration  with  a  standard 
potassium  permanganate  solution. 

Method  of  making  Rational  Analysis 

This  may  be  made  in  several  ways,  two  of  which  are  given. 

1.  The  first  consists  in  separating  the  "insoluble  residue"  in  the 
clay,  as  follows:  Two  grams  of  the  material  are  digested  with  twenty 
cubic  centimeters  of  dilute  sulphuric  acid  for  six  or  eight  hours  on  a 
sand-bath,  the  excess  of  acid  being  finally  driven  off. 

One  cubic  centimeter  of  concentrated  hydrochloric  acid  is  now  added 
and  boiling  water.  The  insoluble  portion  is  filtered  off,  and  after  being 
thoroughly  washed  with  boiling  water  is  digested  in  fifteen  cubic  cen- 
timeters of  boiling  sodium  hydroxide  of  ten  per  cent  strength.  Twenty- 
five  cubic  centimeters  of  hot  water  are  added  and  the  solution  filtered 
through  the  same  filter-paper,  the  residue  being  washed  five  or  six 
times  with  boiling  water.  The  residue  is  now  treated  with  hydrochloric 
acid  in  the  same  manner  and  washed  upon  the  filter-paper,  until  free 
from  hydrochloric  acid,  is  burned  and  weighed  as  insoluble  residue. 


CHEMICAL  PROPERTIES   OF  CLAY  67 

The  alumina  found  in  the  portion  insoluble  in  sulphuric  acid  and 
sodium  hydroxide  is  multiplied  by  3.51.  This  factor  has  been  found  to 
represent  the  average  ratio  between  alumina  and  silica  in  orthoclase 
feldspar;  therefore  the  product  just  obtained  represents  the  amount  of 
silica  that  would  be  present  in  undecomposed  feldspar.  The  sum  of 
this  silica  with  the  alumina,  ferric  oxide,  and  alkalies  equals  the  "feld- 
spathic  detritus."  The  difference  between  silica  as  calculated  for  feld- 
spar and  the  total  silica  in  the  insoluble  portion  represents  the  "  quartz  " 
or  "free  sand."  The  difference  between  that  portion  of  the  sample 
insoluble  in  sulphuric  acid  and  sodium  hydroxide  and  the  total  repre- 
sents the  "clay  substance." 

2.  A  second  method,  and  one  used  in  Germany,1  is  conducted  as  fol- 
lows: 

After  five  grams  of  clay  are  weighed  and  placed  in  a  200  c.c.  Erlen- 
meyer  flask,  100-150  c.c.  of  water  and  2  c.c.  of  sodium  hydrate  are 
added,  and  the  contents  boiled,  covering  the  flask  with  a  small  glass 
funnel.  The  contents  of  the  flask  are  allowed  to  cool,  and  25  c.c.  of 
sulphuric  acid  is  added.  Continue  the  boiling  until  ths  fumes  of  the 
acid  begin  to  be  driven  off  the  flask. 

As  a  result  of  the  reactions  which  have  taken  place  the  calcium 
carbonate  has  been  changed  to  calcium  sulphate,  the  aluminum  silicate 
has  been  converted  into  aluminum  sulphate  and  silicic  acid,  while  the 
quartz  and  feldspar  remain.  Water  is  added  to  the  flask  and  most  of 
the  sulphuric  acid  and  aluminum  sulphate  washed  out  of  the  residue  by 
decantation. 

In  washing  by  decantation  the  water  which  is  decanted  should  be 
placed  upon  a  filter-paper,  for  the  reason  that,  should  any  of  the  residue 
be  removed  from  the  flask,  it  can  be  returned  by  making  a  hole  in  the 
filter  and  washing  back  into  the  flask. 

After  washing  by  decantation  the  contents  of  the  flask  are  treated 
with  hydrochloric  acid  (100  c.c.)  and  boiled.  Decant  off  the  liquid  and 
add  sodium  hydroxide  (100  c.c.),  boil  and  decant.  Repeat  the  above 
process  with  hydrochloric  acid  and  sodium  hydrate.  The  residue  is  then 
transferred  to  a  filter  and  washed  with  dilute  hydrochloric  acid  (1  to 
20).  The  filter  with  contents  is  transferred  to  a  platinum  crucible 
and  weight  determined. 

The  contents  of  the  crucible  are  treated  with  a  few  drops  of  sul- 
phuric acid  and  small  quantities  of  hydrofluoric  acid,  evaporated  to 
dryness  in  the  water-bath,  ignited,  weighed,  and  from  the  loss  calculate 

1  Ladenburg,  Handworterbuch  der  Chemie,  12,  p.  15. 


68  CLAYS 

and  determine  aluminum,  iron,  etc.  From  the  aluminum  found  in  the 
residue  the  feldspar  is  calculated,  1  part  of  alumina  (aluminum  oxide)  = 
5.41  of  feldspar. 

Although,  as  pointed  out  above,  the  rational  analysis  is  an  invalu- 
able aid  to  the  investigator  of  high-grade  clays,  still  the  methods  em- 
ployed are  far  from  satisfactory  or  accurate,  for  in  the  treatment  of  the 
clay  with  concentrated  sulphuric  acid  the  feldspar  does  not  remain  un- 
attacked,1  and  the  mica  may  also  be  decomposed. 

This  fact  led  Buckley  2  to  adopt  the  following  method  for  the  Wis- 
consin clays,  which  are  usually  impure  and  often  of  highly  feldspathic 
character.  "The  feldspar  and  kaolinite  were  calculated  from  the  ulti- 
mate analysis,  using  the  following  percentage  compositions  of  feldspar: 
K20,  16.9;  A1203,  18.4;  6Si02,  64.7;  and  Na2O,  11.8;  A12O3,  19.5; 
6Si02,  68.7;  and  kaolinite  as  A12O3,  39.5;  2SiO2,  46.5;  2H2O,  14;  as 
given  by  Dana.3 

"All  the  potash  and  soda  were  figured  to  feldspar.  The  alumina 
required  for  the  feldspar  was  deducted  from  the  total  alumina,  and  the 
difference  was  taken  as  the  starting-point  from  which  to  figure  the  kao- 
linite substance.  The  difference  between  the  total  silica  (Si02)  and  that 
required  by  both  feldspar  and  kaolin  gives  the  quartz  and  the  silica  in 
silicates  other  than  those  mentioned." 


MINERAL  COMPOUNDS  IX  CLAY  AND  THEIR  CHEMICAL  EFFECTS 

All  the  constituents  of  clay  influence  its  behavior  in  one  way  or  another, 
their  effect  being  often  noticeable  when  only  small  amounts  are  present. 
Their  influence  can  perhaps  be  best  discussed  individually. 

Silica  4 

This  is  present  in  clay  in  two  different  forms,  namely,  uncombined 
as  silica  or  quartz  and  in  silicates,  of  which  there  are  several.  Of 
these  one  of  the  most  important  is  the  mineral  kaolinite,  which  probably 
occurs  in  all  clays,  and  is  termed  the  clay  base  or  clay  substance.  The 
other  silicates  include  feldspar,  mica,  glauconite,  hornblende,  garnet,  etc. 
These  two  modes  of  occurrence  of  silica,  however,  are  not  always  dis- 
tinguished in  the  ultimate  analysis  of  a  clay,  but  when  this  is  done  they 
are  commonly  designated  as  "free  "  and  "combined"  silica,  the  former 

1  Langenbeck,  Chemistry  of  Pottery,  pp.  3-12. 

2  Wis.  Geol.  and  Nat.  Hist.  Surv.,  Bull.  7,  Pt.  I,  p.  267,  1901. 
8  Text-book  of  Mineralogy,  pp.  371,  377,  and  481. 

4  See  also  description  of  the  minerals  quartz,  feldspar,  kaolinite,  and  mica  above. 


CHEMICAL  PROPERTIES  OF  CLAY 


69 


referring  to  all  silica  except  that  contained  in  the  kaolinite,  which  is 
indicated  by  the  latter  term.  This  is  an  unfortunate  custom,  for  the 
silica  in  silicates  is,  properly  speaking,  combined  silica,  just  as  much  as 
that  contained  in  kaolinite.  A  better  practice  is  to  use  the  term  sand 
to  include  quartz  and  silicate  minerals  other  than  kaolinite,  which  are 
not  decomposable  by  sulphuric  acid.  In  the  majority  of  analyses,  how- 
ever, the  silica  from  both  groups  of  minerals  is  expressed  collectively  as 
"total"  silica. 

The  percentage  of  both  quartz  and  total  silica  found  in  clays  varies 
between  wide  limits,  as  can  be  seen  from  the  following  examples.  Wheeler 
gives  a  minimum  1  of  5  per  cent  in  the  flint-clays,  and  the  sand  percentage 
as  20  to  43  per  cent  in  the  St.  Louis  clays,  and  20  to  50  per  cent  in  the 
loess-clays.  Twenty-seven  samples  of  Alabama  clays  analyzed  by  the 
writer  contained  from  5  to  50  per  cent  of  insoluble  residue,  mostly  quartz.2 
In  seventy  North  Carolina  clays3  the  insoluble  sand  ranged  from  15.15  to 
70.43  per  cent. 

The  following  table4  gives  the  variation  of  total  silica  in  several 
classes  of  clays,  the  results  being  obtained  from  several  hundred  analyses: 

AMOUNT  OF  SILICA  IN  CLAYS 


Kind  of  clay. 

Per  cent  of  total  silica. 

Min. 

Max. 

Aver. 

Brick-clays  .  .       .... 

34.35 
45.06 
34.40 
32.44 

90.877 
86.98 
96.79 
81.18 

59.27 
45.83 
54.304 
55.44 

Pottery-clays  

Fire-clays  

Kaolins  

The  free  silica  or  quartz  is  one  of  the  commonest  constituents  of  clay, 
and  ranges  in  size  from  particles  sufficiently  large  to  be  visible  to  the 
eye  down  to  the  smallest  grains  of  silt. 

With  the  exception  of  kaolinite,  all  of  the  silica-bearing  minerals 
mentioned  above  are  of  rather  sandy  or  silty  character,  and,  therefore, 
their  effect  on  the  plasticity  and  shrinkage  will  be  similar  to  that  of 
quartz.  In  burning  the  clay,  however,  the  general  tendency  of  all  is  to 
affect  the  shrinkage  and  also  the  fusibility  of  the  clay,  but  their  behavior 
is  in  the  latter  respect  more  individual. 

1  Mo.  Geol.  Surv.,  Vol.  XI,  p.  54. 

2  Ala.  Geol.  Surv.,  Bull.    6,1900. 

3  N.  C.  Geol.  Surv.,  Bull.  13,  p.  24,  1898. 

4  Bull.  N.  Y.  State  Museum,  No.  35,  p.  525. 


70  CLAYS 

Sand  (quartz  and  silicates)  is  an  important  antishrinkage  agent, 
which  greatly  diminishes  the  air-shrinkage,  plasticity,  and  tensile  strength 
of  clay,  its  effect  in  this  respect  increasing  with  the  coarseness  of  the 
material;  clays  containing  a  high  percentage  of  very  finely  divided  sand 
(silt)  may  absorb  considerable  water  in  mixing,  but  show  a  low  air- 
shrinkage.  The  brickmaker  recognizes  the  value  of  the  effects  men- 
tioned above  and  adds  sand  or  loam  to  his  clay,  and  the  potter  brings 
about  similar  results  in  his  mixture  by  the  use  of  ground-flint. 

It  is  thought  by  some  that  because  of  the  refractoriness  of  quartz  its 
addition  to  any  clay  will  raise  its  fusion-point,  but  this  is  true  only 
of  those  clays  containing  a  high  percentage  of  common  fluxes  and  silica 
and  which  are  burned  at  low  temperatures.  Its  effect  on  highly  alum- 
inous low-flux  clays  reduces  their  refractoriness. 

In  considering  the  effects  of  sand  in  the  burning  of  clays,  it  must 
be  first  stated  that  the  quartz  and  silicates  fuse  at  different  tempera- 
tures. A  very  sandy  clay  will,  therefore,  have  a  low  fire-shrinkage  as 
long  as  none  of  the  sand-grains  fuse,  but  when  fusion  begins  a  shrinkage 
of  the  mass  occurs.  We  should,  therefore,  expect  a  low  fire-shrinkage 
to  continue  to  a  higher  temperature  in  a  clay  whose  sand -grains  are 
refractory. 

Of  the  different  minerals  to  be  included  under  sand  the  glauconite 
is  the  most  easily  fusible,  followed  by  hornblende  and  garnet,  mica  (if 
very  fine  grained),  feldspar,  and  quartz.  The  glauconite  would,  there- 
fore, other  things  being  equal,  act  as  an  antishrinkage  agent  only  at  low 
temperatures.  Variation  in  the  size  of  the  grain  may  affect  these  results, 
but  this  point  is  discussed  under  Fusibility  (Chapter  III). 

Hydrous  silica. — From  the  observations  of  W.  H.  Zimmer1  it  would 
appear  that  some  kaolins  carry  hydrated  silicic  acid.  In  a  kaolin  of  the 
composition : 

Silica  (SiO2) 57.00 

Alumina  (A12O3) ' 24.85 

Ferric  oxide  (Fe2O3) 25 

Lime  (CaO) 05 

Water  (H2O) 17.81 

he  found  that  the  rational  analysis  showed  only  0.05  per  cent  not  de- 
composed by  sulphuric  acid,  which  would  lead  one  to  suppose  that  the 
clay  was  a  pure  kaolin.  The  analysis,  however,  disproved  this,  and  led 
to  the  conclusion  that  there  must  be  free  hydrated  silicic  acid.  His 

1  Trans.  Amer.  Cer.  Soc.,  Ill,  p.  25,  1901. 


CHEMICAL  PROPERTIES  OF  CLAY  71 

experiments  with  this  clay,  and  with  artificial  mixtures  containing  silicic 
acid,  showed  that  the  presence  of  any  important  quantity  of  free  hy- 
drated  silicic  acid  in  a  clay  tends: 

1.  To  produce  an  increase  of  translucency  over  that  obtained  where 
the  silica  used  is  all  quartzitic  at  equal  temperatures;  2,  to  bring  about 
an  improvement  in  color;  3,  to  increase  the  shrinkage  both  in  air  and  in 
fire;  4,  to  produce  a  lowering  of  the  temperature  at  which  vitrification 
occurs;  5,  a  tendency  to  warp  in  drying;  6,  a  tendency  to  form  a  hard 
coating  on  the  surface  of  the  clay  or  ware,  due  to  the  deposition  of  H2Si03 
from  water  used  in  making  wares  plastic. 


Iron  Oxide 

Sources  of  iron  oxide  in  clays. — Iron  oxide  is  one  of  the  commonest 
ingredients  of  clay,  and  a  number  of  different  mineral  species  may  serve 
as  sources  of  it,  the  most  important  of  which  are  grouped  below: 

Hydrous  oxide,  limonite;  oxides,  hematite,  magnetite;  silicates, 
biotite,  glauconite  (greensand),  hornblende,  garnet,  etc.;  sulphides, 
pyrite;  carbonates,  siderite. 

In  some,  such  as  the  oxides,  the  iron  is  combined  only  with  oxygen, 
and  is  better  prepared  to  enter  into  chemical  combination  with  other 
elements  in  the  clay  when  fusion  begins.  In  the  case  of  the  sulphides 
and  carbonates,  on  the  contrary,  the  volatile  elements,  namely,  the  sul- 
phuric-acid gas  of  the  pyrite  and  the  carbonic-acid  gas  of  the  siderite, 
have  to  be  driven  off  before  the  iron  contained  in  them  is  ready  to  enter 
into  similar  union.  In  the  silicates  the  iron  is  chemically  combined  with 
silica  and  several  bases,  forming  mixtures  of  rather  complex  composition 
and  all  of  them  of  low  fusibility,  particularly  the  glauconite.  Several 
of  these  silicates  are  easily  decomposed  by  the  action  of  the  weather, 
and  the  iron  oxide  which  they  contain  combines  with  water  to  form 
limonite.  This  is  usually  in  a  finely  divided  condition,  so  that  its  color- 
ing action  is  quite  effective. 

The  range  of  ferric  oxide,  as  determined  from  a  number  of  published 
clay  analyses,  is  as  follows : 1 

AMOUNT  OF  FERRIC  OXIDE  IN  CLAYS 

Kind  of  clay.  Min.  Max.  Aver. 

Brick-clays 0.126  32.12         5.311 

Fire-clays 0.01  7.24         1 .506 

1  Bull.  N.  Y.  State  Museum,  No.  35,  p.  520. 


72  CLAYS 

Effects  of  iron  compounds. — Iron  is  the  great  coloring  agent  of  both 
burned  and  unburned  clays.  It  may  also  serve  as  a  flux  and  even  affect 
the  absorption  and  shrinkage  of  the  material. 

Coloring  act  on  of  iron  in  unburned  clay. — Many  clays  show  a  yellow 
or  brown  coloration  due  to  the  presence  of  limonite,  and  a  red  coloration 
due  to  hematite;  magnetite  is  rarely  present  in  sufficient  quantity  to 
color  the  clay;  siderite  or  pyrite  may  color  it  gray,  and  it  is  probable 
that  the  green  color  of  many  clays  is  caused  by  the  presence  of  silicate 
of  iron,  this  being  specially  true  of  glauconitic  ones.  The  intensity  of 
color  is  not  always  an  indication  of  the  amount  of  iron  present,  since 
the  same  quantity  of  iron  may,  for  example,  color  a  sandy  clay  more 
intensely  than  a  fine-grained  one,  provided  both  are  nearly  free  from 
carbonaceous  matter;  the  latter,  if  present  in  sufficient  quantity,  may 
even  mask  the  iron  coloration  completely.  The  coloring  action  will, 
moreover,  be  effective  only  when  the  iron  is  evenly  distributed  through 
a  clay  in  an  extremely  fine  form.  It  is  probable  that  the  limonite  color- 
ing clays  is  present  in  an  amorphous  or  non-crystalline  form,  and  forms 
a  coating  on  the  surface  of  the  grains. 

Coloring  action  of  iron  oxide  on  burned  clay. — All  of  the  iron  ores 
will  in  burning  change  to  the  red  or  ferric  oxide,  provided  a  sufficient 
supply  of  oxygen  is  able  to  enter  the  pores  of  the  clay  before  it  is  vit- 
rified; if  vitrification  occurs  the  iron  oxide  enters  into  the  formation  of 
silicates  of  complex  composition.  The  color  and  depth  of  shade  pro- 
duced by  the  iron  will,  however,  depend  on  first,  the  amount  of  iron 
in  the  clay;  second,  the  temperature  of  burning;  third,  condition  of  the 
iron  oxide,  and  fourth,  the  condition  of  the  kiln  atmosphere. 

1.  Clay  free  from  iron  oxide  burns  white.  If  a  small  quantity,  say 
1  per  cent,  is  present  a  slightly  yellowish  tinge  may  be  imparted  to  the 
burned  material,  but  an  increase  in  the  iron  contents  to  2  or  3  per  cent 
often  produces  a  buff  product,  while  4  or  5  per  cent  of  iron  oxide  in  many 
cases  makes  the  clay  burn  red.  There  seem,  howrever,  to  be  not  a  few 
exceptions  to  the  above  statements.  Thus  we  find  that  the  white-burning 
clays  carry  from  a  few  hundredths  per  cent  to  over  1  per  cent  of  iron 
oxide,1  the  more  ferruginous  containing  more  iron  than  the  purer  grades 
of  buff-burning  clays.  Again,  among  the  buff-burning  clays  we  find 
some  with  an  iron-oxide  content  of  4  or  5  per  cent,  an  amount  equal  to 
that  contained  in  some  red-burning  ones. 

The  facts  would  therefore  seem  to  indicate  that  the  color  of  the 
burned  clay  is  not  influenced  solely  by  the  quantity  of  iron  present. 

1  Seger's  Collected  Writings,  Translation,  I,  p.  109;  also  Orton,  Trans.  Amer. 
Ceram.  Soc.,  V,  p.  380. 


CHEMICAL   PROPERTIES  OF  CLAY  73 

Seger  has  divided  the  buff-burning  clays  into  two  groups,  namely, 
(1)  those  of  such  high  iron  contents  as  to  burn  red  normally,  but  which 
are  sufficiently  calcareous  to  enable  the  lime  to  destroy  the  red  iron  color 
and  form  a  yellow  compound  of  iron  and  lime,  and  (2)  those  low  in  iron 
and  high  in  alumina,  which  would  normally  burn  pale  red,  but  develop 
a  yellow  color  due  to  the  formation  of  an  alumina-iron  compound.  He 
thus  believes  that  the  red  coloration  of  the  iron  is  destroyed  by  similar 
causes,  but  on  account  of  the  lime  being  a  stronger  or  more  active  base 
than  the  alumina  it  is  able  to  take  care  of  a  greater  quantity  of  iron. 

Orton1  has  argued  against  the  effect  of  alumina,  claiming  that  if 
this  were  true  synthetic  mixtures  should  easily  give  the  buff  color  which, 
in  his  experience,  it  is  not  possible  to  produce.  As  he  states,  there  is  a 
great  uniformity  in  the  color  of  buff-burning  clays,  while  their  iron- 
alumina  ratios  fluctuate  greatly;  some  fire-clays  containing  40  per  cent 
of  alumina  and  0.5  per  cent  iron,  and  yielding  a  good  buff  product,  while 
others  with  15  to  20  per  cent  alumina  and  2.5  per  cent  iron  burn  to 
almost  exactly  the  same  tint.  On  the  other  hand,  some  clays  with  about 
the  same  alumina  and  iron  content  burn  red. 

It  would  seem,  therefore,  as  if  the  cause  of  this  buff-burning  quality 
must  be  sought  for  in  some  other  direction. 

The  evenness  of  color  is  apparently  closely  connected  with  the  physi- 
cal condition  of  the  iron  oxide,  that  in  colloidal  form  giving  a  uniformity 
of  shade  not  obtainable  by  the  admixture  of  very  finely  ground  material. 

2.  If  a  clay  is  heated  at  successively  higher  temperatures,  it  is  found 
that,  other  things  being  equal,  the  color  usually  deepens  as  the  tempera- 
ture rises.    Thus,  if  a  clay  containing  4  per  cent  of  iron  oxide  is  burned 
at  a  low  temperature  it  will  be  pale  red,  and  harder  firing  will  be  neces- 
sary to  develop  a  good  brick  red,  which  will  pass  into  a  deep  red  and 
then  reddish  purple. 

Seger  explained  the  successive  shades  of  red  by  assuming  that  the 
iron  oxide  increased  in  density  with  rising  temperature. 

The  brilliancy  of  the  color  appears  to  be  influenced  by  the  texture, 
as  the  more  sandy  clays  can  be  heated  to  a  higher  temperature,  without 
destruction  of  the  red  color,  than  the  more  aluminous  ones.  Alkalies 
also  appear  to  diminish  the  brightness  of  the  iron  coloration.2 

3.  Among  the  oxides  of  iron  two  kinds  are  recognized,  known  respec- 
tively as  the  ferrous  oxide  (FeO)  and  ferric  oxide  (Fe2O3) .    In  the  former 

1  Trans.  Amer.  Ceram.  Soc.,  V,  p.  389,  1903. 

2  Ries,  N.  Y.  State  Mus.,  Bull.  35,  515,  1900;   Orton,  Trans.  Amer.  Ceram.  Soc., 
V,  p.  414,  1903. 


74  CLAYS 

we  see  one  part  of  iron  united  with  one  of  oxygen,  wrhile  in  the  latter 
one  part  of  iron  is  combined  with  one  and  one-half  parts  of  oxygen. 
The  ferric  oxide,  therefore,  contains  more  oxygen  per  unit  of  iron  than 
the  ferrous  salt,  and  represents  a  higher  stage  of  oxidation.  In  the 
limonite  and  hematite  the  iron  is  in  the  ferric  form,  representing  a  higher 
stage  of  oxidation.  In  magnetite  both  ferrous  and  ferric  iron  are  present, 
but  in  siderite  the  ferrous  iron  alone  occurs.  In  the  ultimate  analysis  the 
iron  is  usually  determined  as  ferric  oxide,  no  effort  being  made  to  find 
out  the  quantity  present  in  the  ferrous  form,  although  if  there  is  any 
reason  to  suspect  that  much  of  the  latter  exists  it  should  be  determined. 

Iron  passes  rather  readily  from  the  ferric  to  the  ferrous  form  and 
vice  versa.  Thus,  if  there  is  a  deficit  of  oxygen  in  the  inside  of  the  kiln 
the  iron  does  not  get  enough  oxygen  and  the  ferrous  compound  results, 
but  the  latter  changes  rapidly  to  the  ferric  condition  if  sufficient  air 
carrying  oxygen  is  admitted.  The  necessity  for  recognizing  these  two 
forms  of  iron  oxide  is  because  they  affect  the  color  of  the  clay  differently. 
Ferrous  oxide  alone  is  said  to  produce  a  green  color  when  burned,  while 
ferric  oxide  alone  may  give  purple  or  red,  and  mixtures  of  the  two  pro- 
duce yellow,  cherry  red,  violet,  blue,  and  black.1 

Seger2  found  that  combinations  of  ferric  oxide  with  silica  produced 
a  yellow  or  red  color  in  the  burned  clay.  We  may  thus  get  a  variation 
in  the  color  produced  in  burning  clay,  depending  on  the  character  of 
oxidation  of  the  iron  or  by  mixtures  of  the  two  oxides.3 

Moreover,  in  the  burning  of  ferruginous  clays  it  is  usually  desirable 
to  get  the  iron  thoroughly  oxidized  to  prevent  trouble  in  the  later  stages 
of  burning.  To  accomplish  this  the  iron  must  be  freed  of  any  sulphur 
or  carbon  dioxide  which  may  be  combined  with  it,  and  other  volatile 
or  combustible  elements  in  the  clay  must  be  driven  off,  so  as  to  allow 
the  oxidizing  gases  to  enter  the  clay  and  unite  with  any  ferrous  iron 
that  may  be  present. 

Sulphide  of  iron  (pyrite)  loses  half  its  sulphur  at  a  red  heat,  and  the 
balance  will,  under  oxidizing  conditions,  pass  off  probably  by  900°  C., 
while  siderite  or  ferrous  carbonate  loses  its  carbon  dioxide  between  400° 
and  500°  C.;  magnesium  carbonate  and  calcium  carbonate  lose  their 
CO2  at  about  500°  C.  and  800°  to  900°  C.  respectively.  Carbonaceous 
matter,  if  present,  must  also  be  carefully  burned  off.  If  the  clay  con- 
tains much  volatile  or  combustible  matter  the  burning  must  proceed 

1  Keramic,  p.  256. 

2  Notizblatt,  p.  16,  1874. 

8  See  "Flashing  of  Brick,"  under  Burning. 


CHEMICAL  PROPERTIES  OF  CLAY  75 

slowly  below  1000°  C.,  in  order  to  remove  it  and  allow  the  iron  to  get 
oxidized  while  the  clay  is  still  porous. 

After  oxidation  the  clays  will  show  a  more  brilliant  iron  color  than 
they  do  at  the  end  of  the  dehydration  period.  They  are  also  harder 
and  show  a  slight  decrease  in  volume. 

If  the  clay  has  been  improperly  oxidized  it  shows  later  when  vitri- 
fication is  reached,  by  the  ferrous  oxide  in  the  center  of  the  brick  forming 
a  fusible  silicate  which  melts  and  evolves  gases  that  swell  up  the  ware. 

In  some  cases  improper  oxidation  is  shown  by  the  presence  of  a  black 
core  in  the  center  of  the  brick. 

Fine-grained  clays  are  more  difficult  to  oxidize  than  coarse-grained 
ones,  because  of  the  small  size  of  their  pores,  and  grog  is,  therefore, 
added  at  times  to  open  the  grain  of  the  material. 

4.  Since  the  stage  of  oxidation  of  the  iron  is  dependent  on  the  quan- 
tity of  air  it  receives  during  burning,  the  condition  of  the  kiln  atmos- 
phere is  of  great  importance.  If  there  is  a  deficiency  of  oxygen  in  the 
kiln,  so  that  the  iron  oxide,  if  present,  is  reduced  to  the  ferrous  condition, 
the  fire  is  said  to  be  reducing.  If,  on  the  contrary,  there  is  an  excess  of 
oxygen,  so  that  ferric  oxides  are  formed,  the  fire  is  said  to  be  oxidizing. 
These  various  conditions  are  often  used  by  the  manufacturer  to  produce 
certain  shades  or  color-effects  in  his  ware.  Thus,  for  example,  the  manu- 
facturer of  flashed  brick  produces  the  beautiful  shading  on  the  surface 
of  his  product  by  having  a  reducing  atmosphere  in  his  kiln  followed  by 
an  oxidizing  one.  The  potter  aims  to  reduce  the  yellow  tint  in  his  white 
ware  by  cooling  the  kiln  as  quickly  as  possible  to  prevent  the  iron  from 
oxidizing. 

Fluxing  action  of  iron  oxide. — Iron  oxide  is  a  fluxing  impurity,  lower- 
ing the  fusing-point  of  a  clay,  and  this  effect  will  be  more  pronounced  if 
the  iron  is  in  a  ferrous  condition  or  if  silica  is  present.  In  burning  a  clay 
.at  low  temperatures  the  hydrous  ferric  oxide  (limonite)  loses  its  water 
of  hydration.  Heating  the  clay  to  vitrification  in  a  reducing  atmosphere 
is  believed  to  produce  a  ferrous  silicate,  which  is  seen  on  the  brown, 
black,  or  greenish  glassy  portion  of  the  surface  of  paving  brick  and 
unglazed  sewer-pipe.1  When  well-vitrified  bricks  show  a  red  color  it  is 
thought  by  some  that  the  iron  oxide  is  merely  dissolved  in  the  vitri- 
iied  mass  and  has  not  entered  into  combination,  i 

A  low  iron  content  is,  therefore,  desirable  in  refractory  clays,  and 
the  average  of  a  number  of  analyses  of  these  shows  it  to  be  1.3  per  cent. 
Brick-clays,  which  are  usually  easily  fusible,  contain  from  3  to  7  per  cent 
of  iron  oxide.  i 

1  la.  Geol.  Surv.,  XIV,  59,  1904. 


76  CLAYS 

Effect  of  iron  oxide  on  absorptive  power  and  shrinkage  of  clay. — 

So  far  as  the  writer  is  aware  no  experiments  have  been  made  to  discover 
the  increased  absorptive  power  of  a  clay  containing  limonite,  although  the 
clay  soils  show  that  the  quantity  of  water  absorbed  is  greater  with  limonite 
present.  This  greater  absorptive  power  may  be  accompanied  by  an 
increased  shrinkage.  The  fire-shrinkage  might  also  be  great,  because 
of  the  increased  loss  of  combined  water  due  to  the  presence  of  limonite.1 

Lime 

Lime  is  found  in  many  clays,  and  in  the  low-grade  ones  may  be  present 
in  large  quantities.  Quite  a  large  number  of  minerals  may  serve  as 
sources  of  lime  in  clays,  but  all  fall  into  one  of  the  three  following  groups: 

1.  Carbonates.     Calcite,  dolomite. 

2.  Silicates  containing  lime,  such  as  feldspar  and  garnet. 

3.  Sulphates.     Gypsum. 

Whenever  the  ultimate  analysis  of  clay  shows  several  per  cent  of 
lime  (CaO)  it  is  usually  there  as  an  ingredient  of  lime  carbonate  (CaCO3), 
and  in  such  cases  its  presence  can  be  easily  detected  by  putting  a  drop 
of  muriatic  acid  or  vinegar  on  the  clay.2  When  present  in  this  form  it  is 
apt  to  be  finely  divided,  although  it  may  occur  as  concretions  or  lime- 
stone pebbles,  or  as  cylindrical  bodies  along  rootlets. 

The  feldspars  are  the  commonest  source  of  lime  among  the  silicates, 
oligoclase  and  anorthite  being  the  usual  lime-bearing  varieties,  but  the 
amount  of  lime  present  in  silicates  is  usually  very  low. 

When  lime  is  present  as  an  ingredient  of  silicate  minerals,  such  as 
those  mentioned  above,  its  presence  cannot  be  detected  with  muriatic 
acid.  Gypsum,  which  is  found  in  a  few  clays,  is  often  of  secondary  char- 
acter, having  been  formed  by  the  action  of  sulphuric  acid  on  lime-bearing 
minerals  in  the  clay.  Since  these  three  groups  of  minerals  behave  some- 
what differently  their  effects  will  be  discussed  separately. 

Effect  of  lime  carbonate  on  clay. — Lime  is  probably  most  effective 
in  the  form  of  the  carbonate,  and  if  finely  divided  is  an  active  flux.  When 
clays  containing  it  are  burned,  they  not  only  lose  their  chemically  com- 
bined water  but  also  their  carbon  dioxide;  but  while  the  water  of  hyclra- 
tion  passes  off  between  450°  C.  (842°  F.)  and  600°  C.  (1112°  F.)  the  car- 
bon dioxide  (C02)  does  not  seem  to  go  off  until  between  600°  C.  (1112°  F.) 
and  725°  C.  (1562°  F.).  In  fact,  it  more  probably  passes  off  between 

1  See  tests  under  Fire-shrinkage,  Chap.  III. 

2  See  Minerals  in  Clay,  Calcite. 


CHEMICAL  PROPERTIES  OF  CLAY  77 

850°  C.  (1562°  F.)  1  and  900°  C.  (1652°  F.).  The  result  of  driving  off 
this  gas,  in  addition  to  the  chemically  combined  water,  is  to  leave  cal- 
careous clays  more  porous  than  other  clays  up  to  the  beginning  of  fusion.2 

If  the  burning  is  carried  only  far  enough  to  drive  off  the  carbonic- 
acid  gas,  the  result  will  be  that  the  quicklime  thus  formed  will  absorb 
moisture  from  the  air  and  slake.  No  injury  may  result  from  this  if  the 
lime  is  in  a  finely  divided  condition  and  uniformly  distributed  through 
the  brick,  but  if,  on  the  contrary,  it  is  present  in  the  form  of  lumps,  the 
slaking  and  accompanying  swelling  of  these  may  split  the  brick. 

If,  however,  the  temperature  is  raised  higher  than  is  required  simply 
to  drive  off  the  carbon  dioxide,  and  if  some  of  the  mineral  particles  soften, 
a  chemical  reaction  begins  between  the  lime,  iron,  and  some  of  the  silica 
and  alumina  of  the  clay,  the  result  being  the  formation  within  the  clay 
of  a  new  silicate  of  very  complex  composition.  The  effects  of  this  com- 
bination are  several:  In  the  first  place,  the  lime  tends  to  destroy  the 
red  coloring  of  the  iron  and  imparts  instead  a  buff  color  to  the  burned 
clay.  Seger  found  that  this  bleaching  action,  if  we  may  call  it  such,  is 
most  marked  when  the  percentage  of  lime  is  three  times  that  of  the  iron. 
It  should  be  remembered,  however,  that  all  buff-burning  clays  are  not 
calcareous,  and  that  a  clay  containing  a  low  percentage  of  iron  oxide 
may  also  give  a  buff  body.  Another  effect  of  lime,  if  present  in  sufficient 
quantity,  is  to  cause  the  clay  to  soften  rapidly,  thereby  sometimes  draw- 
ing the  points  of  incipient  fusion  and  viscosity  within  41.6°  C.  (75°  F.)  of 
each  other.  This  rapid  softening  of  calcareous  clays  is  one  of  the  main 
objections  to  their  use,  and  on  this  account  also  it  is  not  usually  safe 
to  attempt  the  manufacture  of  vitrified  products  from  them,  but,  as 
mentioned  under  Magnesia,  the  presence  of  several  per  cent  of  the  latter 
substance  will  counteract  this.  It  has  also  been  found  possible  to  increase 
the  interval  between  the  points  of  incipient  fusion  and  viscosity  by  the 
addition  of  quartz  and  feldspar.3 

Many  erroneous  statements  are  found  in  books  regarding  the  allow- 
able limit  of  lime  in  clays,  some  writers  putting  it  as  low  as  3  per  cent; 
still  a  good  building  brick  can  be  made  from  a  clay  containing  as 
much  as  20  or  25  per  cent  of  lime  carbonate,  provided  it  is  in  a  finely 
divided  condition,4  and  a  vitrified  ware  is  not  attempted.  If,  however, 

1  Bourry,  Treatise  on  Ceramic  Industries,  p.  103;  also  Kennedy,  Trans.  Amer. 
Cer.  Soc.,  IV,  p.  146. 

2  Some  bricks  made  from  calcareous  clays   and   burned  at  cones  1  to  3  show 
over  30  per  cent  absorption. 

3  The  Collected  Writings  of  H.  Seger,  Vol.  I,  p.  336. 

4  For  analyses  and  uses  of  calcareous  clays  see  H.  Ries,  Clays  and  Shales  of 


78  CLAYS 

that  quantity  of  lime  is  contained  in  the  clay  in  the  form  of  pebbles,  then 
much  damage  may  result  from  bursting  of  the  bricks,  when  the  lumps 
of  burned  lime  slake  by  absorbing  moisture  from  the  air. 

Clays  containing  a  high  percentage  of  lime  carbonate  are  used  hi 
the  United  States,  especially  in  Michigan,  Wisconsin,  and  Illinois,  for 
making  common  bricks,  common  earthenware,  roofing-tile,  and  some 
terra- cotta,  and  the  highly  calcareous  character  of  some  brick-clays  is 
shown  by  the  following  analyses.  Of  these  No.  II  is  the  most  calcareous 
that  the  writer  has  ever  examined. 

ANALYSES  OF  CALCAREOUS  CLAYS 

I.  II. 

Silica  (SiO2) 44.15  18.62 

Alumina  (A12O3) 10-°°  3-23 

Ferric  oxide  (Fe2O3) 4-08  J-26 

Lime  (CaO) 13.30  41 .30 

Magnesia  (MgO) 1 1 .50  .42 

Potash  (K20) 1.55  {gone 

Soda  (Na2O) By  difif.               2.42 

Water  (H2O) 12.13 

Carbon  dioxide  (CO,,) 11.34              32.50 

Organic  matter 1 . 95 

Total 100.00  99.75 

Total  fluxes 20.43  42.98 

I.  Ionia,  Mich.     A.  N.  Clark,  Anal.  Mich.  Geol.  Surv.,  VIII,  Pt.  I,  p.  53. 
II.  Seguin,  Tex.     O.  H.  Palm,  Analyst. 

Effect  of  lime-bearing  silicates. — The  effect  of  these  is  much  less 
pronounced  than  that  of  lime  carbonate.  They  contain  no  volatile  ele- 
ments, and  hence  do  not  affect  the  shrinkage  to  the  extent  that  lime 
carbonate  does.  They  serve  as  fluxes,1  but  do  not  cause  a  rapid  soften- 
ing of  the  clay. 

Effect  of  gypsum. — Gypsum  in  clay  has  probably  often  been  formed 
by  sulphuric  acid,  liberated  by  the  decomposition  of  iron  pyrite,  acting 
on  lime  carbonate.  Lime,  if  present  in  the  form  of  gypsum,  seems  to 
behave  differently  from  lime  in  the  form  of  carbonate,  although  few 
clays  contain  large  percentages  of  it. 

Gypsum,  as  already  shown,2  is  a  hydrous  sulphate  of  lime.    In  cal- 

Michigan,  Mich.  Geol.  Surv.,  VIII,  Pt.  I;  and  E.  R.  Buckley,  Clays  and  Clay  Indus- 
tries of  Wis.,  Wis.  Geol.  Surv.,  Bull.  2,  Economic  Series. 

1  See  also  under  Alkalies. 

2  Chapter  III,  Minerals  in  Clay. 


CHEMICAL  PROPERTIES  OF  CLAY 


79 


cining  gypsum  for  making  plaster  of  Paris,  the  chemically  combined 
water  is  driven  off  at  250°  C.,  but  only  a  portion  of  the  sulphuric  acid 
is  driven  off  at  a  low  red  heat,  the  balance  passing  off  at  a  much  higher 
temperature.  To  illustrate  this  a  mixture  1  consisting  of  75  per  cent  of  a 
white-burning  clay  and  25  per  cent  of  nearly  pure  white  gypsum  was 
made  up.  This  mixture  contained  15.11  per  cent  of  combined  water 
and  11.65  per  cent  of  sulphur  trioxide  (S03),  and  was  burned  at  a 
number  of  different  temperatures  with  the  following  results: 

TABLE  SHOWING  Loss  IN  WEIGHT  BY  BURNING 


Temperature. 

Loss  in  weight,  per  cent. 

Sample  No.  1. 

Sample  No.  2. 

860°  C    (1580°  F  )  

11.60% 
13.18% 
19.93% 
23.15% 
23.21% 

11.50% 
12.59% 
19.58% 
23.05% 
23.11% 

1000°  C   (1832°  F  )  

1  100°  0   (2012°  F  )  

1200°  C   (2192°  F.)  

1300°  C   (2372°  F.)  

These  figures  show  that  at  860°  C.  the  loss  had  not  exceeded  the  amount 
of  combined  water  contained  in  the  mass;  at  1000°  C.  the  loss  was  not 
equal  to  the  sum  of  the  water  contained  in  the  clay  and  gypsum;  a  large 
loss  occurred  between  1100°  and  1200°  C.,  while  between  the  latter 
temperature  and  1300°  C.  the  loss  was  exceedingly  small.  Therefore, 
even  at  1300°  C.,  or  slightly  above  the  theoretic  melting-point  of  cone  8, 
there  was  still  over  3  per  cent  of  what  would  be  considered  volatile  ma- 
terial remaining  in  the  mixture.  It  is  presumed  that  this  represents 
sulphur  trioxide  which  has  not  been  driven  off. 

The  presence  of  silica  is  said  to  facilitate  the  decomposition  of  the 
calcium  sulphate,  and  the  evolution  of  the  SO3  is  thought  to  cause  some 
of  the  swelling  or  blistering  seen  in  some  wares  after  burning. 

The  range  of  lime,  as  determined  from  a  series  of  clay  analyses,  is  as 
follows:2 

AMOUNT  OP  LIME  IN  CLAYS 


Kind  of  day. 

Min. 

Max. 

Aver. 

0.024 

15.38 

1.513 

0.011 

9.90 

1.098 

0.03 

15.27 

0.655 

tr. 

2.58 

0.47 

1  N.  J.  Geol.  Surv.,  VI,  p.  63,  1904. 

2  Bull.  N.  Y.  State  Museum,  No.  35,  p.  523.     Owing  to  an  error  in  the  analysis 
of  one  of  the  brick-clays,  the  averages  in  this  table  have  been  recalculated. 


80  CLAYS 

Magnesia 

Magnesia  (MgO)  rarely  occurs  in  clay  in  larger  quantities  than  1  per 
cent.  When  present,  its  source  may  be  any  one  of  several  classes  of 
compounds,  that  is,  silicates,  carbonates,  and  sulphates. 

In  the  majority  of  clays  the  silicates,  no  doubt,  form  the  most  im- 
portant source,  and  minerals  of  this  type  carrying  magnesia  are  the 
black  mica  or  biotite,  hornblende,  chlorite,  and  pyroxene.  These  are 
scaly  or  bladed  minerals,  of  more  or  less  complex  composition,  and  con- 
taining from  15  per  cent  to  25  per  cent  of  magnesia.  The  biotite  mica 
decomposes  readily,  and,  its  chemical  combination  being  thus  destroyed, 
the  magnesia  is  set  free,  probably  in  the  form  of  a  soluble  compound, 
which  may  be  retained  in  the  pores  of  the  clay.  Hornblende  is  probably 
not  an  uncommon  constituent  of  some  clays,  especially  in  those  which 
are  highly  stained  by  iron,  and  have  been  derived  from  dark-colored 
igneous  rocks.  Like  biotite,  it  alters  rather  rapidly  on  exposure  to  the 
weather.  Dolomite,  the  double  carbonate  of  lime  and  magnesia,  is  no 
doubt  present  in  some  clays,  and  would  then  serve  as  a  source  of  mag- 
nesia. Magnesium  sulphate,  or  Epsom  salts,  probably  occurs  sparingly 
in  clays,  and  might  form  a  white  coating  either  on  the  surface  of  clay 
spread  out  to  weather,  or  else  on  the  ware  in  drying.  It  is  most  likely 
to  occur  in  those  clays  which  contain  pyrite,  the  sulphide  of  iron 
(FeS2),  for  the  decomposition  of  the  latter  would  yield  sulphuric  acid, 
which,  by  attacking  any  magnesium  carbonate  in  the  clay,  might  form 
magnesium  sulphate.  This  substance  has  a  characteristic  bitter  taste. 
On  heating,  both  magnesium  carbonate  and  dolomite  lose  their  CC>2  be- 
tween 400°  C.  and  600°  C. 

Magnesia  was  for  many  years  regarded  as  similar  to  lime  in  its  fluxing 
action.  The  experiments  of  Mackler l  have  indicated,  however,  that 
its  effect  was  quite  different. 

In  order  to  prove  this  point  he  selected  a  clay  which  was  free  from 
lime  or  magnesia,  and  in  its  raw  and  burned  condition  had  the  composi- 
tion shown  at  top  of  page  81. 

To  one  hundred  parts  by  weight  of  this  clay,  either  lime  or  magnesium 
carbonate  was  added  in  the  proportions  given  in  the  second  table  on 
page  81,  the  percentages  given  in  parenthesis  representing  the  quantity 
of  lime  or  magnesia  contained  in  the  amount  of  carbonate  added.  The 
physical  tests  of  these  mixtures  are  also  given. 

It  will  be  seen  here  that  the  effect  of  magnesia  was  quite  different 

1  Thonindustrie-Zeitung,  Vol.  XXVI,  p.  706,  1904. 


CHEMICAL  PROPERTIES  OF  CLAY 


81 


Loss  on  ignition 

Silica  (SiO2) 

Alumina  (AlgOg) 

Ferric  oxide  (Fe2O3).  . 

Lime   (CaO) 

Magnesia  (MgO) 

Alkalies   (Na2O,  K2O) 


ANALYSIS  OF  CLAY  USED  BY  MACKLER 

Raw. 

, 7.07 

63.25 

22.97 

4.98 


Burned. 


68.06 

24.72 

5.36 


2.07 
100.34 


from  that  exerted  by  the  lime.  The  mixtures  containing  magnesia  did 
not  vitrify  suddenly,  as  did  the  limy  clays ;  nor  did  the  magnesia  exert 
as  strong  a  bleaching  action  on  the  iron,  and  the  points  of  incipient 
fusion  and  viscosity  were  also  separated. 

PHYSICAL  TESTS  ON  MACKLER'S  MIXTURES 


1 

i 

83 

M 

a 

'«  ti 

Fire-shrinkage  cone  numbers. 

t/3 

•c 

*4-f    C 

£5- 
38 

M 

t& 

£ 

<J 

3 

010 

05 

1 

3 

5 

A  Clay  alone  

28.8 

6  4 

9.8 

0  1% 

3  5 

7  2 

7  9 

6  7 

B.  Clay  +  25  CaCO3  (14CaO)  
C.  Clay  +  12.5  CaCO3  (7  CaO)  
D  clay  +  21  MgCO3  (lOMgO)  

31.1 
33.6 
34  0 
32.4 

8.4 
8.3 
8.2 
7.5 

14.3 
10.4 
16.3 
11.1 

1.4 
1.0 
0.6 
1.7 

1.8 
1.7 
3.0 
3.7 

11.1 

ll!3 

* 
t 

E.  Clay  +10.5  MgCO3  (5MgO)  

*  Melted. 


t  Warped. 


With  a  mixture  of  kaolin  and  magnesia  similar  results  were  obtained. 
The  mixture  of  kaolin  and  magnesia  showed  a  higher  shrinkage  at  the 
beginning  of  the  burning  than  the  kaolin  alone,  and  then  increased  but 
little  until  a  high  temperature  was  reached,  when  the  shrinkage  sud- 
denly began  again.  A  hard  body  was  obtained  at  cone  1  with  the  kaolin- 
magnesia  mixture. 

The  effect  of  magnesia  therefore,  if  present  in  sufficient  quantity,  is 
to  act  as  a  flux  and  make  the  clay  soften  slowly,  instead  of  suddenly  as 
in  the  case  of  calcareous  clays.  The  results  mentioned  above  have  been 
corroborated  in  this  country  by  Hottinger.  An  important  characteristic 
of  magnesian  clays  is,  that  they  can  be  made  into  wares  of  extreme  length 
and  very  thin  walls,  which  may  be  nearly  vitrified  without  warping.1 

Barringer2  has  pointed  out  that  the  action  of  magnesia  depends 


1  Hottinger,  Trans.  Amer.  Cer.  Soc.,  V,  p.  130,  1903. 

2  Trans.  Amer.  Cer.  Soc.,  VI,  p.  86,  1904. 


82 


CLAYS 


largely  on  the  composition  of  the  clay;  in  bodies  containing  a  number 
of  active  fluxes,  and  which  vitrify  at  a  low  temperature,  it  has  a  marked 
influence  on  the  fusing  point  and  temperature  of  the  vitrifying  stage, 
but,  "as  the  number  and  character  of  the  bases  change  in  going  towards 
high  fire-products,  the  influence  of  magnesia  lessens  considerably." 

The  range  of  magnesia  in  several  classes  of  clays,  as  figured  from  a 
number  of  analyses,  is  as  follows:1 

AMOUNT  OF  MAGNESIA  IN  CLAYS 


Quality. 

Min. 

Max. 

Aver. 

Brick  clays  

0  02 

7.29 

1    052 

0.05 

4.80 

0  85 

0.02 

6.25 

0  513 

Kaolins  

tr. 

2.42 

0  223 

Alkalies 

The  alkalies  commonly  present  in  clays  include  potash  (K2O),  soda 
(Na2O),  and  ammonia  (NH3).  There  are  other  alkalies,  but  they  are 
probably  of  rare  occurrence. 

Ammonia  is  no  doubt  present  in  some  raw  clays,  judging  from  their 
odor,  and  it  may  possibly  exert  some  effect  on  the  physical  structure 
of  the  clay,  it  being  found  that  the  bunches  of  grains  in  a  clay  tend  to 
separate  more  easily,  when  the  clay  is  agitated  with  water,  if  a  few  drops 
of  ammonia  are  added.  As  ammonia  is  easily  volatile,  it  leaves  the  clay 
as  soon  as  the  latter  is  warmed,  and  therefore  plays  no  part  in  the  burn- 
ing of  the  clay.  The  two  other  common  alkaline  substances,  potash  and 
soda,  are  more  stable  in  their  character,  and  are  therefore  sometimes 
termed  fixed  alkalies.  These  have  to  be  reckoned  with  in  burning,  for 
they  are  present  in  nearly  every  clay. 

The  amount  of  total  fixed  alkalies  contained  in  a  clay  varies  from  a 
mere  trace  in  some  to  9  per  cent  in  others.  The  range  of  alkalies  hi  sev- 
eral classes  of  clays  was  determined  to  be  as  follows : 2 

AMOUNT  OP  TOTAL  ALKALIES  IN  CLAYS 

Min.  Max.  Aver. 

Kaolins 0.1  6.21  1.01 

Fire-clay 0.048  5.27  1.46 

Pottery-clays 0.52  7.11  2.06 

Brick-clays 0. 17  15.32  2.768 

1  Bull.  N.  Y.  State  Museum,  No.  35,  p.  524.     Owing  to  an  error  in  an  analysis 
of  a  brick-clay,  the  figures  in  this  table  have  been  recalculated. 

2  Bull.  35,  N.  Y.  State  Museum,  p.  515. 


CHEMICAL  PROPERTIES  OF  CLAY  83- 

Several  common  minerals  may  serve  as  sources  of  the  alkalies.  Feld- 
spar may  supply  either  potash  or  soda.  Muscovite,  the  white  mica, 
contains  potash.  Greensand,  or  glauconite,  contains  potash.  Other 
minerals,  such  as  hornblende  or  garnet,  might  serve  as  sources  of  the 
alkalies,  but  are  unimportant,  as  they  are  rarely  present  in  clays  in 
large  quantities. 

Orthoclase,  the  potash  feldspar,  contains  17  per  cent  of  potash  (K20), 
while  the  lime-soda  feldspars  contain  from  4  to  12  per  cent  of  soda  (Na20), 
according  to  the  species.  The  lime-soda  feldspars  fuse  at  a  lower  tem- 
perature than  the  potash  ones,  but  are  also  less  common.1 

Muscovite  mica  contains  nearly  12  per  cent  of  potash,  and  may 
contain  a  little  soda.  Muscovite  flakes,  if  heated  alone,  seem  to  fuse 
at  cone  12,  but,  when  mixed  in  a  clay,  they  appear  to  act  as  a  flux  at 
different  temperatures,  according  to  the  size  of  the  grains.  If  very 
finely  ground,  the  mica  appears  to  vitrify  the  body  at  as  low  a  tem- 
perature as  cone  4,2  but  if  the  scales  are  larger  they  will  retain  their 
individuality  up  to  cone  8,  or  even  10.  The  latter  is  true,  for  example,  of 
micaceous  talc-like  clays  found  in  the  Miocene  formation  around  Woods- 
town,  N.  J.,  a  large  amount  of  which  are  composed  of  white  mica.3 

We  therefore  see  that  the  minerals  supplying  alkalies  are  all  silicates 
of  complex  composition.  Each  has  its  fixed  melting-point,  and  the  tem- 
perature at  which  the  alkalies  flux  with  the  clay  will  depend  on  the 
containing  mineral,  and  also  on  the  size  of  the  grains.  If  the  alkali- 
bearing  mineral  grains  decompose,  the  potash  or  soda  are  set  free  and 
form  soluble  compounds.4 

Alkalies  are  considered  to  be  the  most  powerful  fluxing  materila 
that  the  clay  contains,  and,  if  present  in  the  form  of  silicates,  are  a  de- 
sirable constituent,  except  in  clays  of  a  refractory  character.  On  account 
of  their  fluxing  properties  they  serve,  in  burning,  to  bind  the  particles 
together  in  a  dense,  hard  body,  and  permit  a  white  ware,  made  of  porous- 
burning  clays,  to  be  burned  at  a  lower  temperature.  In  the  manufacture 
of  porcelain,  white  earthenware,  encaustic  tiles,  and  other  wares  made 
from  white-burning  clays  and  possessing  an  impervious  or  nearly  im- 
pervious body,  feldspar  is  an  important  flux. 

According  to  the  experiments  of  Berdel  5  on  kaolin,  quartz,  feldspar 
bodies,  the  action  of  feldspar  on  the  vitrification  of  bodies  is  noticeable 

1  Seger,  Ges.  Schrift,  p.  413. 

2  Trans.  American  Ceramic  Society,  IV,  p.  255. 

3  Ries,  N.  J.  Geol.  Surv.,  Fin.  Rept.,  VI,  p.  68,  1904. 

4  See  Origin  of  Clay,  Chapter  I. 

5  Sprechsaal,  Nos.  2-11,  1904. 


84  CLAYS 

at  cone  1,  but  its  effect  on  high-heat  bodies  starts  with  the  melting-point 
of  feldspar  at  cone  9.  The  vitrifying  action  of  feldspar  becomes  greater 
the  finer  the  grain  is,  and  to  such  an  extent  that  very  fine  feldspar  may 
vitrify  Zettlitz  kaolin  at  cone  2. 

Alkalies  alone  seem  to  exert  little  or  no  coloring  influence  on  the 
burned  clay,  although  in  some  instances  potash  appears  to  deepen  the 
color  of  a  ferruginous  clay  hi  burning. 

Titanium 

Titanum  is  an  element  which  is  found  in  several  minerals,  some  of 
which  are  more  common  in  clays  than  is  usually  imagined,  although 
they  appear  rare  because  they  are  seldom  found  in  large  quantities. 
The  two  commonest  of  these,  rutile  and  ilmenite,  have  already  been  re- 
ferred to.  So  far  as  known,  neither  of  these  is  ever  found  in  clays  in 
sufficiently  large  grams  to  be  visible  to  the  naked  eye,  so  that  a  micro- 
scopic examination  would  be  necessary  to  identify  them.  Although 
titanium  is  such  a  common  constituent  of  clay,  it  is  rarely  shown  in 
.an  analysis,  because  its  determination  by  chemical  methods  is  attended 
with  more  or  less  difficulty  and  is  rarely  carried  out.  In  the  ordinary 
process  of  chemical  analysis  it  is  usually  included  with  the  alumina. 

As  early  as  1862  Riley  1  referred  to  the  universal  occurrence  of  titanic 
oxide  in  clay,  and,  in  a  series  of  English  ones,  found  from  .42  to  1.05  per 
cent.  Since  that  time  a  number  of  additional  occurrences  have  been 
noted,  as  follows: 

Twenty-one  New  Jersey  clays,  1.06  to  1.93  per  cent.2 

A  series  of  Pennsylvania  clays,  .85  to  4.30  per  cent.3 

Eleven  Ohio  coal-measure  clays,  0.16  to  1.68  per  cent.4 

Fire-clays  from  St.  Louis,  1  to  1.91  per  cent.5 

Thirty-five  clays  and  sands  from  Virginia  Coastal  Plain,  .0  to  1.88 
per  cent.6 

One  hundred  Texas  clays,  .0  to  2.12  per  cent.7 

Among  the  foreign  observers,  Vogt  8  has  noted  percentages  as  high 

1  Quart.  Jour.  Chem.  Soc.,  XV,  311,  1862. 

2  Cook  and  Smock,  Report  on  the  Clays  of  New  Jersey,  1878,  p.  276. 

3  Second  Pa.  Geol.  Surv.,  MM,  p.  261  et  seq. 

4  Orton,  Ohio  Geol.  Surv.,  VII,  Pt.  I. 

*  Wheeler,  Mo.  Geol.  Surv.,  XI,  p.  56. 

*  Ries,  Va.  Geol.  Surv.,  Bull.  II. 
7  Unpublished  manuscript. 

3  Tonindustrie-Zeitung,  XXVII,  1247,  1903. 


CHEMICAL   PROPERTIES  OF  CLAY 


85 


as  2.08,  and  Kovar  1  the  unusually  high  percentage  of  10.06,  while  Odern- 
heimer  found  up  to  4.6  per  cent  in  certain  Basaltic  residual  clays  from 
the  Duchy  of  Nassau.  The  fact  that  most  of  it  was  soluble  in  a  20  per 
cent  hydrochloric-acid  solution  would  suggest  its  being  ilmenite. 

Effect  of  titanium. — Messrs.  Seger  and  Cramer,  of  Berlin,2  endeavored 
to  determine  the  effect  of  titanium  on  clay  by  burning  artificial  mixtures 
of  this  material  and  kaolin.  Two  samples  of  Zettlitz  kaolin  (containing 
98.5  per  cent  clay  substance)  were  mixed  with  6.5  per  cent  and  13.3  per 
cent  titanium  oxide  respectively;  both  were  then  heated  to  a  tempera- 
ture above  the  fusing-point  of  iron,  with  the  result  that,  while  the  first 


No.36 


',   33 


VII 


•Kaolii 


'in 


and  Titaniun 


Oxide 


0.5 


5$  Titanium  Oxide 


FIG.   18. — Curve  showing  effect  of  titanium  oxide  on  fusibility  of  clay. 
(After  Ries,  N.  J.  Geol.  Surv.,  VI,  p.  71,  1904.) 

softened  considerably  on  heating  and  showed  a  blue  fracture,  the  second 
fused  to  a  deep-blue  enamel. 

A  second  series  of  mixtures,  consisting  each  of  one  hundred  parts  of 
kaolin,  with  5  per  cent  and  10  per  cent  of  silica  respectively,  showed  no 
signs  of  fusion,  and  burned  simply  to  a  hard  white  body,  thus  indicating 
that  the  titanium  acts  as  a  flux  at  a  lower  temperature  than  quartz. 

More  recently  the  author3  has  shown  that  even  small  amounts  of 
titanium  lower  the  refractoriness  of  a  clay.  In  these  experiments  a  white- 


1  Sprechsaal,  1891,  p.  106. 

2  Seger's  Collected  Writings,  I,  p.  519. 

3  N.  J.  Geol.  Surv.,  Fin.  Rept.,  VI,  p.  71,  1904. 


$6  CLAYS 

burning  sedimentary  clay  fusing  at  cone  34  was  mixed  with  amounts  of 
i,  1,  2,  3,  4,  and  5  per  cents  of  very  finely  ground  rutile. 

These  mixtures  were  then  formed  into  small  cones  and  tested  in 
the  Deville  furnace,  the  results  of  these  tests  being  shown  graphically 
by  the  curve  in  Fig.  18.  In  this  figure  the  vertical  line  at  the  left  rep- 
resents the  cone  number  of  the  Seger  series,1  and  the  horizontal  line  at 
the  bottom  the  per  cent  of  titanium  oxide.  No.  VII,  at  the  extreme 
left,  represents  the  fusion-point  of  the  clay  alone,  while  I,  II,  etc.,  indi- 
cate respectively  the  fusion-points  of  the  clay  and  titanium  mixtures. 
From  this  it  will  be  seen  that  even  one-half  per  cent  of  titanium  oxide 
lowered  the  fusing-point  of  the  clay  half  a  cone,  while  5  per  cent  lowered 
it  two  cones.  All  the  mixtures,  when  heated  to  cone  27,  were  appar- 
ently vitrified,  and  showed  a  deep-blue  fracture.  This  coloration  was, 
Tiowever,  destroyed  by  the  presence  of  a  few  per  cent  of  silica.  At 
lower  temperatures  (cone  8)  a  mixture  containing  5  per  cent  of  titanium 
oxide  burned  yellow. 

Water  in  Clay 

Under  this  head  are  included  two  kinds  of  water:  1.  Mechanically 
-combined  water  or  moisture.  2.  Chemically  combined  water. 

Mechanically  combined  water. — The  mechanically  combined  water 
is  that  which  is  held  in  the  pores  of  the  clay  by  capillary  action,  and  fills 
.all  the  spaces  between  the  clay-grains.  When  these  are  all  small,  the 
clay  may  absorb  and  retain  a  large  quantity,  because  each  interspace 
acts  like  a  capillary  tube.  If  the  spaces  exceed  a  certain  size,  they  will 
no  longer  hold  the  moisture  by  capillary  action,  and  the  water,  if  poured 
on  the  clay,  would  fast  drain  away.  The  fine-grained  clays,  for  these 
reasons,  show  high  powers  of  absorption  and  retention,  while  coarse, 
sandy  clays  or  sands  represent  a  condition  of  minimum  absorption. 
This  same  phenomenon  shows  itself  in  the  amount  of  water  required  for 
tempering  a  clay.  Thus,  a  very  coarse  sandy  clay  mixture  from  one 
deposit  required  only  15.9  per  cent  of  water,  while  a  very  fat  one  from 
another  deposit  took  45  per  cent  of  water.  It  is  not  the  highly  aluminous 
ones,  however,  that  always  absorb  the  most  water.  The  total  quantity 
found  in  different  clays  varies  exceedingly.  In  some  air-dried  clays  it 
may  be  as  low  as  0.5  per  cent,  while  in  those  freshly  taken  from  the 
bank  it  may  reach  30  to  40  per  cent  without  the  clay  being  very 
soft. 

Clay  is  very  hygroscopic,  and  when  thoroughly  dry  greedily  absorbs 

1  See  Fusibility,  Chapter  III. 


CHEMICAL  PROPERTIES  OF  CLAY  87 

moisture  from  the  atmosphere,  indeed  it  may  absorb  as  much  as  10  per 
cent  of  its  weight.1 

Water  held  mechanically  in  a  clay  will  pass  off  partly  by  evaporation 
in  air,  but  can  all  be  driven  off  by  heating  the  clay  to  100°  C.  (212°  F.). 
The  evaporation  of  the  mechanical  water  is  accompanied  by  a  shrinkage 
of  the  mass,  which  ceases,  however,  when  the  particles  have  all  come  in 
contact  and  before  all  the  moisture  is  driven  off,  because  some  remains 
in  the  pores  of  the  clay.  This  last  portion  is  driven  off  during  the  early 
stages  of  burning.  The  shrinkage  that  takes  place  when  the  mechanical 
water  is  driven  off  varies — ranges  from  1  per  cent  or  less  in  very  sandy 
clays  up  to  10  or  12  per  cent  in  very  plastic  ones. 

Since  most  clays  having  a  high  absorption  shrink  a  large  amount 
in  drying,  there  is  often  danger  of  their  cracking,  especially  if  rapidly 
dried,  owing  to  the  rapid  escape  of  the  water- vapor.  Mechanical  water 
may  hurt  the  clay  in  other  ways.  Thus,  if  the  material  contains  any 
mineral  compounds  which  are  soluble  in  water,  the  latter,  when  added 
to  the  clay,  will  dissolve  a  portion  of  them  at  least.  During  the  drying 
of  the  brick  the  water  rises  to  the  surface  to  evaporate  and  brings  out 
the  compounds  in  solution,  leaving  them  behind  when  it  vaporizes.  It 
may  also  help  the  fire-gases  to  act  on  certain  elements  of  the  clay,  a 
point  explained  under  Burning 

Chemically  combined  water. — Chemically  combined  water,  as  its 
name  indicates,  is  that  which  exists  in  the  clay  in  chemical  combination 
with  other  elements,  and  which,  in  most  cases,  can  be  driven  out  only 
at  a  temperature  ranging  from  400°  C.  (752°  F.)  to  600°  C.  (1112°  F.).2 
This  combined  water  may  be  driven  from  several  minerals,  such  as 
kaolinite,  which  contains  nearly  14  per  cent,  white  mica  or  muscovite 
with  4  to  5£  per  cent,  and  limonite  with  14.5  per  cent.  Unless  a  clay 
contains  considerable  limonite  or  hydrous  silica,  the  percentage  of 
combined  water  is  commonly  about  one  third  the  percentage  of  alum- 
ina found  in  the  clay.  In  pure,  or  nearly  pure  kaolin,  there  is  nearly  14 
per  cent,  and  other  clays  contain  varying  amounts,  ranging  from  this 
down  to  3  or  4  per  cent,  the  latter  being  the  quantity  found  in  some 
very  sandy  clays.  The  loss  of  its  combined  water  is  accompanied  by  a 
slight  but  variable  shrinkage  in  the  clay,  which  reaches  its  maximum 
some  time  after  all  the  volatile  matters  have  been  driven  off. 

In  many  clay  analyses  the  chemically  combined  water  is  determined 

1  Seger's  Collected  Writings,  I,  p.  214. 

2  See  Bourry,  Treatise  on  Ceramic  Industries,  p.  103;    also  W.  M.  Kennedy, 
Trans.  Amer.  Cer.  Soc.,  IV,  p.  146;   and  further  experiments  under  Fire-shrinkage 
(Chapter  III). 


88  CLAYS 

as  loss  on  ignition,  which  is  incorrect  if  the  clay  contains  carbon  dioxide 
sulphur  trioxide,  or  organic  matter,  all  of  which  are  driven  off,  in  part 
at  least,  at  a  dull  red. 

Carbonaceous  Matter 

Under  this  head  is  included  all  matter  of  carbonaceous  character, 
most  of  which  is  of  vegetable  origin.  Few  sedimentary  clays  are  entirely 
free  from  it,  the  material  having  become  incorporated  with  the  clay  dur- 
ing its  deposition.  Although  when  first  mixed  with  the  clay  it  may  have 
been  more  or  less  fresh,  it  has  since  then  often  undergone  changes  due 
to  burial  within  the  clay  out  of  direct  contact  with  the  air,  which  have 
imparted  to  it  an  asphaltic  or  a  coaly  character. 

Carbonaceous  material  may  occur  in  clay  in  three  different  forms, 
namely : 

1.  Vegetable  tissue,  such  as  wood,  leaves,  stems,  etc.,  in  which  form 
it  is  but  slightly  altered,  and  when  of  this  character  is  commonly  found 
in  surface  clays  of  recent  origin.    Organic  matter  of  this  character  rarely 
affects  the  color  of  the  raw  clay  and  burns  out  easily,  so  that  it  causes 
but  little  trouble;  then,  too,  it  is  usually  present  in  but  small  amounts, 
rarely  exceeding  1  per  cent. 

2.  Carbonaceous  matter  of  asphaltic  or  bituminous  character.    This 
burns  readily  at  a  low  red  heat,  because  of  the  highly  combustible  gases 
given  off  from  it.    It  is  found  in  some  clays  and  in  many  shales,  especially 
those  associated  with  coal-seams,  and  in  the  shales  which  are  worked 
may  range  anywhere  from  0  to  10  per  cent.     If  it  increases  above  this 
the  shales  are  not  workable.    Even  5  to  6  per  cent  causes  much  trouble 
in  burning. 

3.  Hard,  or  coaly  carbon,  resembling  anthracite.    This  burns  slowly, 
and  gives  off  few  combustible  gases. 

Effects  of  carbon  in  clay. — Only  the  second  and  third  of  the  groups 
mentioned  need  to  be  considered.  The  first  alone  causes  trouble  when 
it  occurs  in  the  form  of  sticks  or  thick  roots  and  has  to  be  screened  out. 
It  is,  therefore,  not  included  in  what  follows. 

Carbonaceous  matter  often  serves  as  a  strong  coloring  agent  of  raw 
clays.  If  present  in  small  amounts  it  tinges  them  gray  or  bluish  gray, 
while  larger  quantities  cause  a  black  coloration.  Indeed,  so  strong  may 
this  be  that  it  masks  the  effect  of  other  coloring  agents  such  as  iron.  In 
fact,  two  clays  colored  black  might  burn  red  and  white  respectively, 
because  one  had  much  iron  and  the  other  none,  and  yet,  owing  to  their 
black  color,  this  could  not  be  foretold  with  definiteness. 


CHEMICAL  PROPERTIES  OF  CLAY  89 

Asphaltic  carbon,  aside  from  its  coloring  action,  often  causes  much 
trouble  in  burning,  causing  black  cores,  or  even  swelling  and  fusing  of 
the  brick.  More  than  this,  it  may  keep  the  iron  in  a  ferrous  condition 
and  prevent  the  development  of  the  best  color-effects  in  the  ware. 

The  reason  for  this  is  due  to  several  causes: 

Carbon  has  a  strong  affinity  for  oxygen,  much  stronger  than  that  of 
iron,  therefore  as  long  as  it  remains  in  the  clay  it  will  monopolize  the 
supply  of  oxygen  and  keep  the  iron  in  a  ferrous  condition,  the  form 
in  which  much  of  it  is,  in  gray  or  black  clays  and  shales.  Now,  in  burn- 
ing a  clay,  one  of  the  aims  of  the  clay-worker  is  to  get  the  iron  into  a 
ferric  condition,  so  as  to  fully  develop  its  coloring  properties  and  prevent 
other  troubles.  As  long  as  any  carbonaceous  matter  remains  the  oxida- 
tion of  the  iron  is  prevented  or  retarded,  and  consequently  the  carbon 
must  be  burned  out. 


FIG.  19. — Changes  in  burning  a  black  clay  to  a  buff-colored  brick.  The  lightest 
one  was  not  removed  from  kiln  until  all  the  carbon  was  burned  off.  (After 
Ries,  N.  J.  Geol.  Surv.,  Fin.  Rept.,  VI,  p.  140,  1904.) 

The  experiments  of  Orton  and  Griffin  l  have  shown  that  between 
800°  and  900°  C.  is  the  best  temperature  interval  for  burning  off  the 
carbon,  as  below  this  the  oxidation  of  it  does  not  proceed  as  rapidly, 
and  above  this  there  is  danger  of  vitrification  beginning  and  the  oxida- 
tion being  stopped. 

The  method  of  procedure  would  therefore  be  to  drive  all  moisture 
out  of  the  clay  first,  then  raise  the  heat  as  rapidly  as  possible  to  a  tem- 


1  Second    Report    of    Committee    on    Technical    Investigation,    Indianapolis, 
1905. 


90  CLAYS 

perature  between  800°  and  900°  C.,  and  hold  it  there  until  the  ware 
no  longer  shows  a  black  core  denoting  ferrous  iron. 

In  order  to  burn  off  the  carbon  and  oxidize  the  iron,  air  supplying 
oxygen  must  be  drawn  into  the  kiln  during  burning,  for  the  gases  of 
combustion  from  the  fuel  will  supply  none.  Oxidation  may  be  accelerated 
by  increasing  the  amount  of  ah-  entering  the  kiln  and  by  reducing  the 
density  of  the  clay  as  much  as  possible. 

In  case  this  is  not  done,  and  the  pores  of  the  clay  close  up  before  all 
the  carbon  is  burned  off,  the  expansion  of  the  gases  given  off  by  the 
carbon  will  bloat  the  clay  up  as  soon  as  it  becomes  soft,  and  this  may 
be  even  followed  by  complete  fusion  of  the  interior  of  the  mass,  caused 
by  the  formation  of  an  easily  fusible  ferrous  silicate.  When  the  carbon 
is  all  burned  off  then  the  iron  has  a  chance  to  oxidize. 

If  the  clay  contains  much  asphaltic  carbon,  then  the  oxidation  must 
be  carried  on  with  as  little  air  as  possible,  otherwise  the  heat  generated 
by  the  burning  hydrocarbons  may  be  so  intense  as  to  vitrify  the  ware 
before  the  oxidation  is  completed. 

Since  dense  clays  are  more  difficult  to  oxidize  than  porous  ones,  the 
process  of  manufacture  may  also  influence  the  results,  and  in  this  con- 
nection it  has  been  found  that  bricks  made  by  the  soft-mud  process  are 
most  rapidly  oxidized,  followed  by  either  the  stiff-mud  or  dry- press 
(there  being  no  difference  between  the  two),  and  lastly  by  the  semi- 
dry-press. 

Effect  of  water  on  black  coring. — It  is  often  stated  by  brickmakers 
that  black  cores  are  caused  by  the  brick  being  set  too  wet.  This  is  not 
strictly  true,  and  the  relation  is  but  a  very  indirect  one.  While  carbon 
burns  off  most  rapidly  between  the  temperatures  of  800°  and  900°  C., 
still  it  also  passes  off  somewhat  at  much  lower  temperatures.  If  now 
the  brick  is  set  wet  it  requires  so  much  more  heat  in  the  early  stages  of 
firing  to  drive  out  or  evaporate  the  water  that  other  changes,  such  as 
the  oxidation  of  the  carbon,  will  be  retarded,  and  brick  begins  to  vitrify 
before  the  process  is  completed. 

Soluble  Salts 

Origin. — It  has  been  pointed  out  in  Chapter  I  (Origin  of  Clay)  that 
in  the  decomposition  of  mineral  grains  in  clay  soluble  compounds  are 
often  formed.  During  the  drying  of  the  clay  the  moisture  brings  these 
to  the  surface  and  leaves  them  there  when  it  evaporates,  thus  forming 
a  scum  on  the  air-dried  ware,  and  sometimes  a  white  coating  on  the  clay 
after  it  is  burned.  Those  found  in  the  clay  are  commonly  sulphates  of 


CHEMICAL  PROPERTIES  OF  CLAY  91 

lime,  iron,  or  alkalies,  and  their  formation  is  generally  due  to  the  de- 
composition of  the  iron  pyrite  frequently  contained  in  the  clay.  A  much 
greater  quantity  of  soluble  sulphates  will  be  formed  if  the  pyrite  is  in  a 
finely  divided  condition  and  evenly  distributed  through  the  clay,  but 
these  compounds  may  also  be  formed  without  the  aid  of  pyrite,  as  when 
the  carbonates  are  set  free  by  the  decomposition  of  silicates  such  as  feld- 
spar. When  the  soluble  compounds  have  formed  in  the  green  clay  their 
presence  can  often  be  detected  by  spreading  the  dug  clay  out  to  weather, 
which  will  result  in  their  forming  a  crust  on  the  surface  of  the  mass. 

Their  formation  does  not  cease,  however,  when  they  are  removed 
from  the  ground,  for  in  some  cases  fresh  pyrite  grains  remain  in  the  clay 
after  mixing,  and  if  the  clay  is  stored  in  a  moist  place  these  may  de- 
compose, yielding  an  additional  amount  of  soluble  material.  One  means 
of  preventing  this  would  seem  to  be  to  use  the  clay  as  soon  as  possible 
after  mixing. 

In  some  cases  soluble  sulphates  may  be  even  introduced  into  the 
clay  by  the  water  used  for  tempering,  for  distilled  water  is  the  only  kind 
that  is  free  from  soluble  salts.  All  well  and  spring  waters  contain  some 
gft  least,  and  if  these  flow  or  drain  from  clays  or  rocks  containing  any 
pyrite  they  are  almost  sure  to  contain  soluble  salts.  Those  flowing  from 
lime  rocks  are  usually  "hard,"  on  account  of  the  lime  carbonate  which 
they  contain.  Still  another  source  of  soluble  salts  in  raw  clay  lies  in 
some  of  the  artificial  coloring  materials  which  are  sometimes  used. 

Soluble  sulphates  are  sometimes  formed  in  burning,  through  the 
use  of  sulphurous  fuel,  that  is,  coal  containing  more  or  less  iron  pyrite. 
When  the  coal  is  burned  part  of  the  sulphur  in  the  pyrite  is  expelled, 
and,  uniting  with  the  oxygen,  forms  sulphuric-acid  gas  (SO3).  This 
passes  through  the  kiln,  and,  if  it  comes  in  contact  with  carbonates  in 
the  clay,  converts  them  into  sulphates,  because  some  substances,  such 
as  lime  (CaO),  have  a  stronger  affinity  for  sulphur  trioxide  (SO3)  than 
for  carbon  dioxide  (CO2). 

It  frequently  happens  that  clay  products  come  from  the  kiln  ap- 
parently free  from  any  superficial  discoloration  or  coating,  but  develop 
one  later  on  if  subjected  to  moisture.  In  this  case  the  salts  have  been 
formed  within  the  body  of  the  ware  during  burning,  and  are  brought 
to  the  surface  by  the  evaporation  of  moisture  absorbed  during  rainy 
weather. 

Mackler l  found  that,  in  a  series  of  fifty  bricks  examined,  the  sum  of 
the  sulphates  of  lime,  magnesium,  and  alkalies  varied  from  .0134  per 
<cent  to  .7668  per  cent. 

1  Thonindustrie-Zeitung,  No.  43,  1904. 


92  CLAYS 

The  coatings  thus  far  mentioned  are  all  white  in  color.  In  some 
instances,  however,  the  product  becomes  covered  with  a  yellow  or  green 
stain,  which  is  caused  either  by  the  growth  of  vegetable  matter  on  the 
surface  of  the  bricks,  or  by  soluble  compounds  of  the  rare  element  vana- 
dium. Some  white  coatings  seen  on  brick,  however,  come  from  the 
mortar. 

Quantity  of  soluble  salts  in  a  clay. — The  amount  of  soluble  salts 
present  in  a  clay  is  never  very  great,  but  less  than  0.1  per  cent  is  often 
sufficient  to  produce  a  white  incrustation. 

Prevention  of  soluble  salts. — If  a  brick  is  vitrified  the  soluble  com- 
pounds are  rendered  insoluble,  but  in  the  manufacture  of  many  grades 
of  ware  the  clay  is  not  carried  to  vitrification,  and  therefore  the  soluble 
salts  must  be  rendered  insoluble  if  possible.  This  is  most  effectively 
done  by  adding  some  chemical  to  the  wet  clay  which  will  react  with 
the  soluble  salts  in  it,  and  either  render  them  insoluble  or  else  change 
them  into  some  very  easily  soluble  compound  that  can  be  readily  washed 
from  the  surface  of  the  ware. 

The  substance  commonly  added  is  either  barium  chloride  or  barium 
carbonate.  When  barium  salts  come  in  contact  with  soluble  sulphates/ 
barium  sulphate  is  formed,  a  combination  which  is  insoluble  in  water. 
This  is  expressed  by  the  first  of  the  following  chemical  reactions  if 
barium  carbonate  is  used,  and  by  the  second  if  barium  chloride  is  em- 
ployed : 

1 .  CaSO4 +  BaCO3  =  CaCO3  +  BaSO4. 

2.  CaSO4  +  BaCl2  =  CaCl2  +  BaSO4. 

We  thus  see  that  in  both  cases  we  get  compounds  which  are  insoluble, 
or  nearly  so.  If  soluble  sodium  compounds  are  present,  the  addition  of 
barium  carbonate,  or  barium  chloride,  will  form  either  sodium  carbonate 
or  sodium  chloride  (common  salt),  but  since  both  of  these  are  easily 
soluble  in  water  they  can  be  washed  off  without  much  trouble. 

Method  of  use. — As  carbonate  of  barium  is  insoluble  in  water,  in 
order  to  make  it  thoroughly  and  uniformly  effective  it  should  be  used 
in  a  finely  powdered  condition  and  distributed  through  the  clay  as 
thoroughly  as  possible,  because  it  will  only  act  where  it  comes  into  im- 
mediate contact  with  the  soluble  sulphates.  While  only  a  small  quan- 
tity of  barium  is  necessary,  still  it  is  desirable  to  use  somewhat  more  than 
is  actually  required. 

According  to  Gerlach,1  a  clay  containing  0.1  per  cent  sulphate  of 
lime,  which  is  the  same  as  0.4  grams  per  pound,  would  need  0.6  of  a 
gram  of  barium  carbonate  per  pound  of  clay.  For  safety,  however, 
1  The  Brickbuilder,  1898,  p.  59  et  seq. 


CHEMICAL  PROPERTIES  OF  CLAY  93 

6  or  7  grams  should  be  added  to  every  pound  of  clay.  This  would  be 
about  100  pounds  for  every  thousand  bricks,  based  on  the  supposition 
that  a  green  brick  weighs  7  pounds.  As  a  pound  of  barium  carbonate 
costs  about  two  and  one-half  cents,  the  amount  of  it  required  for  1000 
bricks  would  be  $2.50.  It  is  cheaper  to  use  barium  chloride,  for  the 
reason  that  the  salt  is  soluble  in  water,  and  hence  can  be  distributed 
more  evenly  with  the  use  of  a  smaller  quantity;  the  chemical  reaction 
also  takes  place  much  more  rapidly  when  it  is  used.  There  is  this  objec- 
tion to  it,  however,  that  as  near  the  theoretic  amount  as  possible  must 
be  used;  for  if  any  remains  in  the  clay  unchanged,  that  is,  without  hav- 
ing reacted  with  the  soluble  salts,  it  may  of  itself  form  an  incrustation. 

In  the  case  of  a  clay  containing  0.1  per  cent  calcium  sulphate  it  would 
require  26  pounds  of  barium  chloride  per  thousand  bricks,  and  this,  at 
two  and  one-half  cents  a  pound,  would  mean  an  outlay  of  $0.65.  With 
the  barium-chloride  treatment,  chloride  of  lime  is  formed,  but  this  is 
•decomposed  in  burning. 

Since,  in  drying  molded-clay  objects,  the  evaporation  is  greatest  from 
the  edges  and  corners  of  the  ware,  the  incrustations  may  be  heaviest  at 
these  points,  but  the  more  rapidly  the  water  is  evaporated  the  less  will 
be  the  quantity  of  soluble  salts  deposited  on  the  surface.  Incrustations 
which  appear  during  drying  are  found  more  commonly  on  bricks  made 
from  very  plastic  clays,  which,  owing  to  their  density,  do  not  allow  the 
water  to  evaporate  quickly. 


CHAPTER  III 
PHYSICAL  PROPERTIES  OF  CLAY 

Introductory. — Under  Physical  Properties  there  are  included  plas- 
ticity, texture,  tensile  strength,  shrinkage,  porosity,  specific  gravity, 
fusibility,  color,  slaking,  absorption. 

Plasticity 

Definition. — Plasticity  is  probably  by  far  the  most  important  property 
of  clay,  lacking  which  it  would  be  of  comparatively  little  value  for  the 
manufacture  of  clay  products.  Seger1  has  defined  it  as  the  property 
which  solid  bodies  show  of  absorbing  and  holding  a  liquid  in  their  pores, 
and  forming  a  mass  which  can  be  pressed  or  kneaded  into  any  desired 
shape,  which  it  retains  when  the  pressure  ceases,  and,  on  the  withdraawl 
of  the  water,2  changes  to  a  hard  mass.  The  term  hard  of  course  refers 
to  its  hardness  as  compared  with  its  wet  condition,  for  some  air-dried 
clays  are  rather  soft. 

This  is  a  somewhat  narrow  interpretation  of  the  property  of  plasticity, 
and  one  which  would  practically  exclude  anything  except  very  plastic 
clays. 

A  broader  conception,  and  probably  a  more  satisfactory  one  to  the 
physicist,  would  be  to  define  plasticity  as  the  property  which  many 
bodies  possess  of  changing  form  under  pressure,  without  rupturing, 
which  form  they  retain  when  the  pressure  ceases,  it  being  understood 
that  the  amount  of  pressure  required,  and  the  degree  of . deformation 
possible,  will  vary  with  the  material. 

Plasticity  is  not  a  property  of  clays  alone,  for,  as  pointed  out  by  B. 
Zschokke  3  in  connection  with  his  study  of  the  methods  of  testing  it, 

1  Beziehungen  zwischen  Feuerfestigkeit  und  Plasticitat  der  Tone. — Thonindustrie- 
Zeitung,  1890,  p.  201. 

2  By  evaporation. 

3  Thonindustrie-Zeitung,  No.  120,  p.  1658,   1905;    and  Baumaterialienkunde, 
1902,  No.  24,  25-26;  1903,  Nos.  1-2,  3-4,  and  5-6. 

94 


PHYSICAL  PROPERTIES  OF  CLAY  95 

other  bodies,  such  as  lead  and  wax,  are  plastic  in  their  natural  condition 
at  ordinary  temperatures,  while  copper,  steel,  and  glass  are  plastic  at 
higher  temperatures. 

Others,  like  clay  and  some  mineral  aggregates,  are  plastic  only  when 
wet,  but  even  then  vary  greatly  in  their  plasticity. 

Some  writers  on  clay,  in  attempting  to  give  examples  of  plastic  and 
non-plastic  bodies,  have  sought  to  compare  clay  and  sand,  stating  that 
the  latter,  even  when  fine-grained  and  wet,  shows  no  plasticity;  and, 
while  it  is  true  that  a  very  fine-grained  wet  sand,  or  a  finely  ground 
mass  of  quartz,  does  not  under  pressure  show  the  same  amount  of  deform- 
ability  without  rupture  as  clay,  still  it  shows  some,1  and  the  question  may 
be  asked  whether  both  are  not  classifiable  as  plastic  bodies,  the  one  but 
slightly  plastic  and  the  other  highly  so.  It  is  indeed  possible  to  get  a 
series  of  samples  showing  a  complete  gradation  from  a  highly  plastic 
clay  to  a  but  slightly  plastic  ground  quartz.  The  latter  will  moreover 
hold  its  shape  when  dry,  even  though  it  will  stand  practically  no  handling 
without  breaking. 

Instead,  therefore,  of  intimating  that  plasticity  when  wet  is  a  property 
peculiar  to  clay,  it  would  perhaps  seem  more  correct  to  state  that  this 
property  is  highly  developed  in  clays  as  compared  with  other  earthy  and 
sandy  materials  of  very  fine  grain. 

The  amount  of  water  required  to  develop  the  maximum  plasticity 
in  any  clay  varies  with  the  material,  this  being  shown  by  Wheeler2 
for  a  number  of  Missouri  clays  and  shales,  as  follows: 

Kind.  Per  cent. 

Loess,  or  brick-clay 16-19 

Fire-  and  potters'  clay 15-33 

Flint-clay 15-24 

Kaolins 18-35 

Shales 14-25 

An  important  character,  closely  dependent  on  the  degree  of  plasticity 
exhibited  by  finely  textured  mineral  aggregates,  is  the  assumption  of 
a  more  or  less  hard  condition  when  dry,  the  degree  of  hardness  increasing 
usually  with  the  plasticity. 

Hardening  on  exposure  to  heat  is  not  necessarily  a  function  of 
plasticity,  but  is  due  to  the  particles  softening  by  fusion  and  becoming 
welded  together.  In  those  highly  plastic  mineral  aggregates  (our  most 

1  See  G.  P.  Merrill,  Non-metallic  Minerals,  p.  221. 

2  Mo.  Geol.  Surv.,  XI,  p.  98,  1896. 


96  CLAYS 

plastic  clays)  this  hardening  takes  place  at  a  comparatively  low  tempera- 
ture, because  the  particles  are  very  fine-grained  and  come  into  the  closest 
contact,  thereby  facilitating  heat  reactions;  while,  in  the  coarser-grained 
ones,  the  particles  are  not  only  more  or  less  separated  by  interspaces, 
but  there  are  more  quartzose  grains,  which  of  themselves  are  refractory, 
and  therefore  heat  reactions  occur  at  higher  temperatures,  or  else,  if 
any  fusion  occurs  at  a  lower  heat,  it  is  insufficient  to  bind  the  mass 
together  into  an  impervious  body. 

Cause  of  plasticity  in  clay. — Scientists  have  for  a  long  time  sought 
to  discover  the  cause  of  this  most  interesting  physical  property,  and, 
while  many  theories  have  been  advanced,  none  are  wholly  satisfactory. 
The  more  important  ones  are  referred  to  below. 

Water-of-hydration  theory. — It  has  been  held  by  many  that  the 
plasticity  of  a  clay  stood  in  close  relation  to  the  hydrated  silicate  of 
alumina,  kaolinite,  and  that,  when  the  water  of  combination  of  this 
mineral  was  driven  off,  the  plastic  quality  of  the  clay  disappeared  with 
it.  Indeed,  so  firm  a  hold  has  this  theory  obtained  that  even  to  the 
present  day  it  is  still  quoted  in  many  instances. 

While  it  is  true  that  heating  the  clay  to  a  sufficiently  high  tempera- 
ture to  drive  off  the  chemically  combined  water  causes  a  loss  of  its 
plastic  qualities,  still  these,  so  far  as  known,  stand  in  no  relation  whatever 
to  the  amount  of  kaolinite  present,  and  it  is  more  probable  that  a  tempera- 
ture necessary  to  drive  off  the  water  of  combination  may  also  break  up 
other  structures  closely  related  to  the  plasticity.  Then,  too,  some  of 
the  most  highly  plastic  clays  contain  but  a  very  small  percentage  of 
the  hydrated  silicate  of  alumina. 

As  bearing  against  the  hydration  theory,  we  find  that  two  clays  of 
practically  identical  composition  may  differ  widely  in  their  plastic 
qualities.  Thus,  for  example,  a  white  residual  clay  from  Webster,  N.  C., 
was  found  to  be  decidedly  less  plastic  than  a  white  sedimentary  clay 
from  Edgar,  Fla.,  although  the  two  agreed  closely  in  their  chemical 
composition  and  contained  over  98  per  cent  of  clay  substance.1 

Texture  theory. — Among  the  theories  advanced  to  explain  the 
cause  of  plasticity  is  that  of  fineness  of  grain.  Mr.  Whitney,  for  example, 
in  studying  soils,  has  designated  as  clay  all  those  portions  which  were 
under  .005  mm.  in  diameter.2 

While  it  is  true  that  the  clayey  particles  of  clays  consist  of  grains 
of  all  sizes  below  the  limits  mentioned  above,  still  plasticity  cannot  be 


Ries,  Md.  Geol.  Surv.,  IV,  p.  248,  1902. 

Mechanical  Analysis  of  Soils,  Dept.  of  Agric.,  Bur.  of  Soils,  Bull.  4,  p.  15,  1896. 


PHYSICAL   PROPERTIES   OF  CLAY  97 

explained  on  this  ground  alone.  Very  finely  ground  quartz,  feldspar 
or  mica  are  slightly  plastic,  but  not  nearly  as  much  so  as  most  clays. 
Moreover,  the  finest-grained  clays  are  not  always  the  most  plastic  ones. 
Wheeler  1  has  noted  that  samples  of  quartz  and  limestone  ground  suffi- 
ciently fine  to  pass  a  200-mesh  sieve  felt  plastic  when  wet,  but  fell  to 
pieces  when  dry,  and  the  same  results  were  obtained  by  Orton  2  with 
glass  ground  to  exceeding  fineness.  When  we  recollect,  however,  that 
clay  particles  are  smaller  than  .0001  mm.,  0.02  in.  (0.508  mm.)  is  not 
sufficiently  fine  grinding  for  testing  the  accuracy  of  the  theory.  That 
fineness  no  doubt  exerts  some  influence  on  plasticity  is  evidenced  by 
the  fact  that  fairly  plastic  clays  can  often  be  rendered  more  plastic  by 
fine  grinding,  and  the  addition  of  sand  is  said  by  Beyer  and  Williams  to 
injure  plasticity  directly  as  the  diameter  of  the  grains  increases.3 

On  the  other  hand  Wheeler  found  that  finely  ground  gypsum  and 
brucite  had  considerable  binding  power  and  plasticity,  but  in  this  case 
the  plasticity  was  not  ascribed  to  fineness  alone. 

In  this  connection  we  may  point  to  the  researches  of  Daubre*e,  who 
claimed  that  feldspar,  ground  wet,  gradually  became  plastic  if  allowed  to 
stand,  but  that  dry-ground  feldspar  lacked  plasticity,  and  from  this 
Olchewsky  has  reasoned  that  it  is  prolonged  contact  of  the  mineral 
grains  with  water  during  their  sedimentation  that  develops  plastic 
qualities  in  the  mass. 

A  somewhat  unique  modification  of  this  theory  has  been  proposed 
by  E.  Linder,4  who  considers  that  the  particles  are  of  extreme  fineness, 
and  that  weathering  produces  very  long  or  round  particles,  the  former  ^/ 
giving  greater  contact  surface,  and  thereby  increasing  the  surface  tension 
and  the  plasticity.  He  also  believes  that  if  clays  have  rounded  particles 
they  will  burn  dense  only  at  high  temperatures,  while  in  those  clays 
whose  particles  are  elongated  the  reverse  occurs. 

Plate  theory. — Johnson  and  Blake  5  advanced  the  theory  that  most 
plastic  clays  seem  to  be  composed  largely  of  small  transparent  plates, 
which  were  bunched  together.  They  state: 

"We  have  examined  microscopically  twenty  specimens  of  kaolins, 
pipe-  and  fire-clays.  ...  In  them  all  is  found  a  greater  or  less  propor- 
tion of  transparent  plates,  and  in  most  of  them  the  plates  are  abundant, 
evidently  constituting  the  bulk  of  the  substance. 

1  Mo.  Geol.  Surv.,  XI,  p.  102,  1896. 

2  Brick,  Vol.  XIV,  p.  216. 

3  la.  Geol.  Surv.,  XIV,  p.  86,  1904. 

4  Thonindustrie-Zeitung,  XXXVI,  p.  382. 
6  Amer.  Jour.  Sci.  (2),  p.  351,  1876. 


98  CLAYS 

"The  plasticity  of  a  clay  is  a  physical  character,  and  appears  to  have 
close  connection  with  the  fineness  of  the  particles.  The  kaolinite  of 
Summit  Hill,  consisting  of  crystal  plates  averaging  .003  of  an  inch  in 
diameter,  is  destitute  of  this  quality.  The  nearly  pure  kaolinite  from 
Richmond,  Va.,  occurring  mostly  in  bundles  of  much  smaller  dimensions, 
the  largest  being  but  .001  of  an  inch  in  diameter,  is  scarcely  plastic.  .  .  . 
The  more  finely  divided  fire-clay  from  Long  Island  is  more  'fat/  while 
the  Bodenmais  porcelain  earth,  and  other  clays  in  which  the  bundles 
are  absent  and  the  plates  are  extremely  small,  are  highly  plastic." 

Other  investigators  appear  to  have  attributed  the  cause  of  the  plas- 
ticity to  these  plates,  for  this  same  view  was  advanced  in  1878  by  Bieder- 
mann  and  Herzfeld,1  and  in  this  country  a  similar  view  was  held  by 
Cook,2  who  considered  the  plasticity  to  be  due  to  the  plates  of  kaolinite-. 
He  noted  the  bunched  character  of  these  in  some  clays,  and  pointed  out 
that  attrition  broke  up  these  bunches  and  increased  the  plasticity. 

Haworth,3  in  examining  the  Missouri  clays,  found  the  most  plastic 
clays  to  be  composed  of  minute  scales,  and  Wheeler  4  sought  to  prove 
this  point  experimentally  by  finely  grinding  minerals  possessing  a  plate- 
like  structure.  Calcite  and  gypsum  when  finely  ground  were  found  to 
develop  good  plasticity  when  mixed  with  water,  and  to  have  tensile 
strengths  when  air-dried  of  100  and  350  Ibs.  per  sq.  in.  respectively. 
Talc  and  pyrophyllite  were  likewise  plastic  when  finely  ground  and 
mixed  with  water,  but  developed  little  strength  when  dry. 

Interlocking-grain  theory. — Olchewsky5  was  probably  the  first  to 
suggest  that  the  plasticity  and  cohesion  of  a  clay  were  dependent  on 
the  interlocking  of  the  clay  particles  and  kaolinite  plates,  and  in  this 
connection  used  the  briquette  method  of  testing  the  plasticity,  or  rather 
obtaining  a  numerical  expression  for  it,  by  determining  the  tensile 
strength  of  the  air-dried  clay. 

More  recently  two  Russian  investigators,  U.  Aleksiejew  and  P.  A. 
Cremiatschenski,  in  studying  the  Russian  clays  6  have  come  to  the  con- 
clusion that  plasticity  is  due  not  only  to  the  interlocking  of  the  clay 
particles,  but  varies  also  with  the  fineness  of  the  grain,  the  extreme 
coarse  and  fine  ones  both  having  less  plasticity. 

If  the  tensile  strength  of  a  clay  depends  on  the  degree  of  interlocking 

1  Bischof,  Die  Feuerfesten  Thone,  p.  23. 

2  N.  J.  Geol.  Surv.,  Report  on  Clays,  1878,  p.  287. 

3  Mo.  Geol.  Surv.,  Vol.  XI,  p.  104,  1896. 

4  Ibid.,  p.  106,  1896. 

6T6pf.  u.  Zieg,  Zeit.,  No.  29,  1882. 

8  Zap.  imp.  russk.  techn.  obschtsch.,  1896,  XXX,  pt.  6-7. 


PHYSICAL  PROPERTIES  OF  CLAY  99 

of  the  clay  particles,  then  the  tensile  strength  should  afford  us  a  means 
of  expressing  numerically  the  plasticity  of  the  clay.  It  appears,  however, 
that  there  is  no  such  constant  relation  between  these  two  properties. 

Ball  theory. — Aaron  suggested  that  the  plasticity  of  clay  was  due 
to  the  presence  of  globular  particles,  but  Zschokke  has  with  reason 
disputed  this,  on  the  ground  that  if  the  grains  were  of  this  form  they 
would,  when  in  closest  contact  (as  when  air-dried),  touch  at  the  fewest 
number  of  points, — a  condition,  therefore,  not  favorable  to  the  great 
cohesion  which  exists  between  the  grains  of  highly  plastic  clays. 

Colloid  theory. — In  the  last  thirty  years  not  a  few  observers  have 
called  attention  to  the  fact  that  many  clays  appear  to  contain  grains 
of  non-crystalline  material,  which  is  apparently  of  colloidal  character. 
It  is  believed  that  these  colloids,  or  glue-like  particles,  which  are  mixed 
with  the  mineral  grains,  form  one  cause  of  plasticity,  in  fact  the  main 
one. 

As  this  theory,  or  a  modification  of  it,  seems  to  have  appealed  to< 
many  investigators,  it  may  be  well  to  discuss  it  in  some  detail. 

The  presence  of  colloids  in  clay  was  suggested  at  a  comparatively 
early  date,  for  Way  1  in  1850,  while  endeavoring  to  explain  the  high 
absorptive  powers  of  clay  for  water,  found  that  this  property  was  destroyed 
by  exposure  to  high  heat,  and  considered  that  it  was  due  to  some  peculiar 
form  or  modification  of  aluminum  silicate  which  formed  the  clayey  or 
impalpable  portion  of  the  soil.  In  searching  for  evidence  he  was  able 
to  prepare  an  artificial  hydrated  sodium  aluminum  silicate  which  pos- 
sessed high  absorptive  properties. 

At  a  somewhat  later  date  (1893),  Van  Bemmelen2  announced,  as 
the  result  of  his  investigations  on  the  inorganic  colloids  or  hydrogels, 
that  "nearly  all  metallic  oxides  and  many  salts  have  the  power  of  entering 
into  that  peculiar  hydrated,  non-crystalline  condition  which  Graham  3 
in  1861  denominated  colloid  or  glue-like.  The  special  hydrogel  which 
Van  Bemmelen  studied  most  minutely  was  that  of  silicic  acid,  although  his 
researches  inctuded  the  oxides  of  copper,  tin,  iron,  aluminum,  etc.,  etc. 
As  a  result  of  these  extensive  investigations  the  author  cited  adopts  the 
suggestion  of  Nageli  of  the  micellian  structure  of  colloids,  that  is  to 
say,  that  these  curious  substances  consist  of  heterogeneous  molecular 

1  Royal  Agric.  Soc.  Jour.,  XI,  1850.     Quoted  by  Cushman,  Trans.  Amer.  Cer. 
Soc.,  VI,  p.  7,  1904. 

2  Zeitschr.  anorg.  Chem.,  V,  p.  466;  XIII,  p.  233;  XVIII,  p.  14;  XX,  p.  185; 
XXII,  p.  313.    Quoted  by  Cushman,  Jour.  Amer.  Chem.  Soc.,  XXV,  No.  5,  May> 
1903. 

3  Phil.  Trans.  (1861),  p.  183.    Quoted  by  Cushman,  I.e. 


100  .  CLAYS 

complexes  which  possess  a  submicroscopical,  web-like,  porous  formation, 
one  of  the  distinguishing  characteristics  of  which  is  the  peculiar  relation 
to  and  dependency  on  water  which  they  exhibit.  The  water-content 
of  these  hydrogels  varies  continually  with  the  temperature  and  the 
vapor  pressure  of  the  atmosphere  in  which  they  find  themselves.  Dried 
at  high  temperatures  up  to  a  certain  critical  point,  they  will  lose  nearly 
all  their  water,  only  to  take  it  back  again  eagerly  when  allowed  to  cool 
in  free  air  or  in  moist  atmospheres.  This  dehydration  and  rehydration 
can  be  repeated  indefinitely,  unless  the  temperature  of  drying  is  carried 
too  high,  when  the  faculty  is  gradually  lost  and  finally  destroyed. 

"The  water  thus  absorbed  is  denominated  'micellian  7  water,  and 
differs  from  hygroscopic  water  in  the  ordinary  sense  of  the  word.  It  is 
absorbed  into  the  particles  of  a  powder  of  an  inorganic  hydrogel  without 
changing  the  physical  appearance  when  under  the  microscope,  while 
hygroscopic  water  is  usually  absorbed  on  the  particles  producing  a 
distinct  appearance  of  wetness." 

Among  the  ingredients  of  clay  which  might  assume  a  colloidal  form 
are  aluminum  hydroxide,  iron  oxide,  hydrated  silicic  acid,  and  organic 
matter.  Some  clays  undoubtedly  contain  large  amounts  of  colloids, 
but  in  others,  as  in  many  common  clays,  it  is  claimed  that  there  is  but 
a  small  proportion  of  ingredients  which  are  capable  of  assuming  the  colloid 
state  by  the  action  of  the  water  alone.1 

Schlossing 2  states  that  in  all  kaolins  there  are  finely  crystalline 
substances  and  colloidal  ones,  which  latter  he  separated  by  treatment 
with  ammoniacal  water,  and  found  them  to  be  singly  refracting,  globular 
aggregates,  but  Kasai,3  on  the  other  hand,  disputed  the  existence  of 
colloidal  matter,  for  he  finds  that  the  apparently  colloidal  bodies  of 
Zettlitz  kaolin  are  doubly  refracting. 

Still  later  P.  Rohland  4  suggested  the  colloidal  nature  of  plasticity, 
while  Van  der  Bellen  5  a  little  later  expressed  a  similar  view. 

Lucas 6  in  commenting  on  Rohland's  observation  calls  attention 
to  the  fact  that  Zettlitz  kaolin  must  have  some  colloidal  matter  because 
it  flows  freely  through  a  die,  and  regards  as  significant  the  fact  that  a 
non-plastic  crystalline  powder  will,  under  pressure,  allow  the  water  to 
be  squeezed  out,  and  will  only  form  a  plastic  mass  when  tragacanth  is 
mixed  with  it. 

1  la.  Geol.  Surv.,  XIV,  p.  90,  1904. 

2  Comp.  rend.  1874,  LXXIX,  pp.  376  and  473. 

3  Die  Wasserhaltigen  Aluminum  Silikate.    Diss.  Munchen,  1896. 

4  Zeitschrift  fur  anorganische  Chemie,  Vol.  XXXI,  Ft.  I,  p.  158,  1902. 

5  Chem.  Zeit.,  XXXVI,  1903. 

e  Geol.  Centralbl.  f.  Min.,  Geol.  u.  Pal.,  No.  2,  p.  33,  1906. 


PHYSICAL  PROPERTIES  OF  CLAY  101 

The  theory  of  Olchewsky  that  plasticity  was  due  to  the  spongy 
porous  nature  of  the  smallest  particles,  which  by  reason  of  pressure 
arrange  themselves  into  a  sort  of  felt,  may  be  regarded  as  admitting 
the  presence  of  colloidal  matter,  but  of  more  definite  character  are  the 
statements  of  Arons1  and  Bischof,  who  suggest  that  plasticity  was  no 
doubt  due  to  some  special  form  of  hydrated  aluminum  silicate,  \\hile 
Seger  2  remarks  further  that  there  is  probably  some  effective  molecular 
arrangement,  which  was  already  fixed  in  the  structure  of  the  parent 
rock. 

In  this  country  the  colloid  theory  seems  to  have  received  little  atten- 
tion. In  studying  the  clays  of  Maryland  the  author3  noted  the  presence 
of  what  he  assumed  were  colloidal  bodies  in  the  highly  plastic  clays, 
and  the  subject  has  been  followed  up  in  greater  detail  by  Cushman,4 
who  believes  that  plasticity  is  due  to  a  "colloid  condition  of  the  fine 
particles,  or  of  some  proportion  of  the  particles  which  go  to  make  up 
the  clay  mass.  These  amorphous  inorganic  particles  possess  a  sub- 
microscopic  structure.  They  absorb  water  eagerly,  and  gradually 
assume  the  coherent  condition  which  causes  in  the  wet  mass  the  quality 
we  call  plasticity." 

In  order  to  prove  the  existence  of  colloids  in  clays,  Cushman  5  pre- 
pared some  silicic  acid.  This  jelly  dries  rapidly  to  a  powder,  which 
is  hydrated  and  loses  or  gains  water  with  changes  in  the  moisture  content 
of  the  atmosphere  in  which  it  stands,  but  if  heated  above  1000°  C.  it 
loses  its  absorptive  power.  Hydrated  colloid  alumina  was  also  prepared 
artificially. 

On  mixing  the  former  with  clay  6  it  was  found  that  the  silicic  acid 
increased  the  binding  power  and  shrinkage  but  not  the  plasticity;  while 
the  alumina  increased  the  plasticity  but  not  the  shrinkage  or  binding 
power. 

A  mixture  of  the  two,  prepared  by  adding  sodium  silicate  (water 
glass)  to  the  solution  of  alum,7  showed  that  its  addition  to  a  clay  increased 
both  its  binding  power  and  plasticity. 

Ries  8  found  that  the  addition  of  one  per  cent  gallotannic  acid  to  a 

1  Dammer,  Chem.  Tech.,  1. 

2  Tonindustrie-Zeitung,  p.  37,  1877. 
3Md.  Geol.  Surv.,  Vol.  IVT  p.  251. 

4  Jour.  Amer.  Chem.  Soc.,  XXX,  p.  5. 
s  Trans.  Amer.  Cer.  Soc.,  VI,  p.  7.  1904. 

6  The  percentage  added  is  not  given. 

7  The  suggested  formula  of  this  mixture  is  XAl2O3>YSiO2,ZH2O. 

8  Trans.  Amer.  Cer.  Soc.,  VI,  p.  44,  1904. 


102  CLAYS 

clay  appeared  not  only  to  increase  its  plasticity  but  also  its  binding 
power. 

Grout  by  using  a  dilute  solution  of  agar-agar  for  tempering  two 
clays  found  that  0.08  per  cent  increased  their  plasticity  approximately 
60  and  36  per  cent  respectively. 

He  dried  the  same  mass,  mixed  it  with  water,  filtered  off  the  latter, 
and  tested  the  clear  filtrate  for  soluble  salts,  but  got  no  jelly,  which 
was  probably  due  to  the  fact,  overlooked  by  him,  that  the  clay  adsorbs 
the  colloidal  material.  (See  Adsorption.) 

Alumina  cream  was  then  tried  instead  of  agar-agar,  and  it  was 
found  that  it  took  3  per  cent  of  the  former  to  raise  the  plasticity  as  much 
as  0.08  per  cent  of  the  latter;  furthermore,  after  air-drying,  powdering, 
and  remixing,  the  plasticity  of  the  mass  dropped  to  its  original  figure. 
Grout  consequently  argues  that  since  plastic  clays  are  not  injured  by 
air-drying,  it  is  evident  that  "such  colloids  as  alumina  cream  do  not 
explain  plasticity,  and  that  some  colloid  is  required  which  will  soften 
in  water  after  air-drying,  a  type  which  is  extremely  rare  in  the  inorganic 
kingdom."  He  says  further:  "The  suggestion  of  Cushman,  that  a 
hydrated  silicate  of  alumina  could  be  precipitated  so  as  to  give  the 
desired  properties,  has  been  carefully  tried,  but  all  resulted  exactly  as 
alumina  cream." 

Grout,  moreover,  questions  the  value  of  detecting  colloids  by  staining 
with  rnethylene  blue,  since  he  finds  that  most  clays  contain  from  1  to  5 
per  cent  of  grains  which  will  take  a  stain  from  rnethylene  blue,  gentian 
violet,  eosine,  or  fuchsine.  Both  fresh  and  dried  silicic-acid  jelly  he 
states  take  the  stain,  but  the  latter  acts  like  quartz  in  decreasing  the 
plasticity.  Weathering,  he  further  claims,  does  not  increase  the  number 
of  grains  capable  of  taking  the  stain. 

It  would  appear  from  what  has  been  said  that  most  clays  contain 
(1)  both  non-plastic  bodies  or  grains,  of  either  crystalline  or  amorphous 
character,  and  (2)  colloids,  which  appear  to  at  least  influence  the 
plasticity. 

If  the  colloids  are  the  main  cause  of  plasticity,  this  fact  is  not  proven 
definitely  either  by  showing  their  presence  in  the  clay  or  by  demon- 
strating that  their  addition  to  an  already  plastic  clay  increases  its 
plasticity. 

On  the  contrary,  it  would  seem  necessary  to  add  them  to  some  fine- 
grained mineral  aggregate  of  exceedingly  low7  plastic  qualities,  and 
by  this  addition  be  able  to  change  it  into  a  thoroughly  plastic  mass. 
A  mass  of  colloidal  material  by  itself  does  not  show  the  solidity  and 
'.cohesiveness  which  a  strongly  plastic  clay  does.  It  is  as  if  it  lacked 


PHYSICAL  PROPERTIES  OF  CLAY  103 

some  strengthening  internal  structure,  such  as  a  mass  of  mineral  grains 
might  supply. 

Molecular-attraction  theories. — Several  writers,  to  be  referred  to 
below,  have  inclined  to  the  theory  that  the  plasticity  of  clay  was  due 
to  molecular  attraction  between  the  clay  particles  themselves  or  between 
the  clay  grains  and  water  surrounding  them. 

Ladd,1  as  a  result  of  his  work  on  the  Georgia  clays,  advocates  the 
theory  that  the  mutual  attraction  between  water  and  clay  particles,  and 
surface  tension  of  the  water-films,  may  exert  an  important  influence  in 
determining  plasticity. 

The  affinity  of  the  clay  particles  for  water  will,  however,  vary  with 
their  chemical  nature; 2  and  particles  of  the  same  material  have  a  varying 
affinity,  under  different  conditions  not  now  well  understood.  Moreover, 
salts  and  organic  matter,  in  solution,  modify  the  value  of  the  surface 
tension  of  the  liquid,  the  former  generally  increasing,  the  latter  decreasing. 
This  latter  seems  an  important  point  for  all  clays  containing  a  variable 
quantity  of  soluble  matter. 

The  importance  of  molecular  attraction  between  the  clay  substance 
and  water  was  looked  on  by  Zschokke  3  as  an  important  cause  of  plasticity, 
he  having  pointed  out  that  since  clay  particles  are  plastic  bodies,  they 
have  greater  attraction  for  water  than  non-plastic  grains  such  as  sand, 
and  that  therefore  the  grains  will  be  surrounded  by  a  thicker  film  of  water 
than  sand-grains  would  be.  The  addition  of  an  excess  of  water  separates 
the  clay-grains  so  far  that  they  are  no  longer  able  to  attract  each  other, 
and  the  mass  loses  much  of  its  cohesiveness.  Moreover  it  is  thought 
that  the  absorption  of  the  water  into  the  pores  of  the  clay  is  accompanied 
by  a  superficial  alteration  of  the  clay  particles,  giving  them  a  gelatinous 
coating,  which  permits  them  to  change  their  form  and  at  the  same  time 
keep  in  close  contact;  a  point  which  is  rather  corroborated  by  the 
experiments  of  Cushman  4  and  Mellor.5  He  finally  suggests  that  plas- 
ticity must  be  dependent  on  (1)  the  size  of  the  smallest  particles; 
(2)  the  form  and  character  of  the  surface;  and  (3)  other  peculiar  properties 
possibly  of  a  molecular  character. 

Grout,6  reasoning  along  somewhat  similar  lines,  believes  that  the 
chief  cause  of  plasticity  is  the  molecular  attraction  depending  on  the 

1  Ga.  Geol.  Surv.,  Bull.  6a,  p.  29,  1898. 

2  Whitney,  U.  S.  Dept.  of  Agric.,  Bull.  No.  4,  1892;  Briggs,  ibid.,  Bull.  10,  1897. 
3 1.  c. 

4  Bull.  U.  S.  Dept.  Agric.,  92,  1905. 

8  Trans.  Eng.  Ceram.  Soc.,  V,  Pt.  I,  p.  72,  1905-6. 

*  W.  Va.  Geol.  Surv.,  Ill,  p.  54,  1906. 


104  CLAYS 

chemical  constitution  of  molecules,  but  that  it  may  be  improved  by  the 
addition  to  the  clay  of  colloids  such  as  tannin,  etc.,  or  such  solutions  as 
ammonia,  alum,  etc. 

While  several  of  these  theories — plate  structure,  colloids,  and  molec- 
ular-attraction theory — have  much  to  commend,  still  there  seem  to 
be  serious  objections  in  many  cases  against  their  being  the  sole  cause  of 
plasticity. 

It  is  urged  that  many  clays  show  little  or  no  plate  structure,  and 
yet  the  evidence  of  Vogt  (p.  47),  Cook  (p.  98),  and  Wheeler  (p.  98) 
certainly  indicate  that  it  must  at  least  be  a  factor  governing  the  plastic 
qualities  of  many  clays. 

Although  the  colloid  theory  may  be  discarded  by  some,  still  the 
experiments  of  Cushman  (p.  101),  Ries  (p.  101),  and  Grout  (p.  102) 
point  to  its  importance. 

The  examination  of  any  extensive  series  of  clays  hardly  seems  to 
bear  out  the  theory  that  any  one  of  the  causes  suggested  is  the  sole  one, 
but  rather  that  plasticity  is  dependent  on  a  combination  of  them. 

Effect  of  bacteria. — Aging  a  clay  mixture,  that  is,  allowing  it  to 
lie  in  cellars  for  six  months  or  a  year,  appears  to  improve  its  plasticity,  and 
it  has  been  suggested  that  this  is  due  to  bacterial  action.  Bacteria 
are  not  uncommon  in  clay,  and  the  prevalent  one,  according  to  Stover,1 
is  believed  to  be  bacillus  sulphureus,  whose  development  is  facilitated 
by  a  temperature  of  37°  to  38°  C. 

Seger,  although  not  referring  to  bacteria,  stated  that  in  the  aging 
of  a  clay  an  acid  was  gradually  developed  by  organic  decomposition, 
which  destroyed  the  alkalinity  of  the  mass  and  was  supposed  to  be 
responsible  for  the  improvement  in  plasticity. 

Since  bacteria  are  known  to  exist  in  clays,  they  may  add  organic 
colloids  (protoplasm)  to  it,  and  thereby  increase  its  plasticity.2 

Weathering  clay. — It  is  a  well-known  fact  that  weathering  a  clay 
often  increases  its  plasticity,  but  this  might  be  due  to  several  causes,  such 
as  mechanical  disintegration  of  the  mass  by  frost,  water  soaking,  the 
oxidation  of  organic  matter,  or  to  the  production  of  colloids  by  hydrolysis 
or  bacterial  action. 

Grinding  may  sometimes  improve  the  plasticity  as  much  as  weath- 
ering. 

1  Trans.  Amer.  Cer.  Soc.,  IV,  p.  185,  1902. 

2  W.  Va.  Geol.  Surv.,  Ill,  p.  47,  1906. 


PHYSICAL   PROPERTIES   OF  CLAY  105 


The  Measurement  of  Plasticity 

Clays  vary  widely  in  their  plasticity,  ranging  from  those  which  are 
very  lean  or  low  in  plasticity  to  those  which  are  very  fat  or  of  high  plas- 
ticity. 

Clay  technologists  have  for  a  long  time  been  searching  for  a  satis- 
factory means  of  measuring  the  plasticity  of  clays,  but  this  seems  to  be 
as  difficult  to  find  as  the  true  cause  of  this  peculiar  property. 

The  methods  which  have  been  developed  fall  into  two  classes,  namely, 
tests  of  the  wet  clay  and  tests  of  the  dry  clay,  the  former  being  probably 
the  more  logical. 

Tests  of  the  wet  clay. — The  commonest  and  most  practical  of 
these  consists  in  feeling  the  clay  between  the  fingers.  It  is  not  entirely 
satisfactory,  but  about  the  only  one  that  can  be  used  in  the  field,  and, 
on  the  whole,  gives  us  an  important  clue  to  the  workability  of  the  clay. 

Bischof  1  suggested  forcing  the  wet  clay  through  a  cylindrical  die, 
and  measuring  the  length  of  the  pencil  extruded  before  it  broke  of  its 
own  weight,  and  a  similar  method  has  been  advised  by  E.  C.  Stover,2 
but  there  are  serious  objections  to  this,  because  the  clay  should  be  worked 
up  into  its  most  plastic  condition  before  testing,  and  there  is  no  means 
of  determining  accurately  when  the  condition  of  maximum  plasticity  has 
been  reached. 

The  use  of  the  Vicat  needle  has  also  been  suggested,  the  operation 
consisting  in  forcing  a  needle  into  the  plastic  clay  by  the  pressure  of  a 
known  weight.  Langenbeck3  states  that  the  proper  consistency  is 
reached  when  the  needle  under  a  weight  of  300  grams  penetrates  to  a 
depth  of  four  centimeters  in  five  minutes.  The  same  principle  is  involved 
in  Ladd's  test,  which  consists  in  suspending  a  plumb-bob  from  one  arm 
of  a  balance  and  allowing  it  to  settle  into  the  moist  clay  for  a  given 
period.4  Both  these  methods  suppose  that  the  more  water  a  clay 
requires  for  mixing  the  higher  its  plasticity,  an  assumption  not  altogether 
correct. 

Another  method  suggested  by  Ladd  5  consists  in  having  two  small 
sheet-iron  troughs  with  perforated  bottoms,  in  the  center  of  which 
are  set  test-tube  brushes,  so  placed  that  the  ends  of  the  brushes  touch 

1  Die  feuerfesten  Thone,  p.  84. 

2  Trans.  Amer.  Cer.  Soc.   VII,  p.  397,  1905. 
8  Chemistry  of  Pottery,  p.  19. 

4  Ga.  Geol.  Surv.,  Bull.  6a,  p.  51,  1898. 
5 Ibid.,  p.  52,  1898. 


106 


CLAYS 


when  the  ends  of  the  troughs  are  in  contact.  The  dry  clay  is  sifted 
into  the  brushes  and  water  absorbed  from  below  until  the  point  of 
saturation  is  reached.  The  pull  required  to  tear  the  column  of  clay 
between  the  brushes  is  measured  by  placing  weights  on  a  scale-pan 
attached  to  one  of  the  troughs  until  the  two  separate. 

The  criticism  urged  against  this  method  is  that  it  gives  little  informa- 
tion regarding  the  plasticity,  but  measures  the  strength  of  the  clay 
through  different  degrees  of  saturation.1 

A  somewhat  detailed  investigation  is  that  of  Zschokke.2  According 
to  him,  it  is  necessary,  in  testing  the  plasticity  of  a  clay,  to  consider  (1)  its 
property  of  deformability;  (2)  its  degree  of  cohesion;  (3)  its  stickiness  or 
adhesiveness. 

The  degree  of  deformability  was  first  tested  by  molding  the  thoroughly 
worked  clay  into  cylinders  60  mm.  high  and  30  mm.  in  diameter,  and 
subjecting  these  to  pressure  applied  at  the  ends  until  cracks  appeared, 
but  this  was  found  to  be  unsatisfactory,  as  some  lean  sandy  clays  were 
deformed  more  than  highly  plastic  ones. 

A  more  satisfactory  method  consisted  in  placing  these  freshly  molded 
cylinders  in  a  specially  designed  machine  and  pulling  them  in  two. 
The  amount  of  expansion  showed  the  degree  of  deformability,  while 
the  force  required  to  pull  the  cylinder  in  two  showed  the  tensile  strength. 
The  product  of  the  two  Zschokke  terms  the  plasticity  coefficient.  It  was 
found  that  higher  figures  were  obtained  by  stretching  the  bar  rapidly, 
or  by  a  succession  of  short  rapid  strokes.  The  following  figures  illustrate 
these  points. 

RUPTURE  EXPERIMENTS 


Slow  pull. 

Jerky  pull. 

Per  cent 

No.  of 
sample. 

Tensile 
strength  0 
kgm.  per 

Deforma- 
bility H  in 
per  cent. 

Plasticity 
coefficient 

13  L 

Tensile 

strength  /? 
kgm.  per 

Deforma- 
bility A  in 
per  cent. 

Plasticity 
coefficient 

0L 

H20 
reg. 

sq.  cm. 

269 

.63 

70 

44.1 

1.73 

127 

220 

29.8 

250 

.48 

28.6 

13.7 

1.52 

97 

147 

22.9 

631 

.42 

18.4 

7.7 

.96 

91 

87 

26.0 

901 

.36 

17.4 

6.3 

.93 

82 

76 

21.8 

705 

.27 

33.4 

9. 

.86 

94 

81 

20.8 

507 

.25 

20. 

5. 

.96 

90 

86 

20.8 

702 

.20 

8.6 

1.7 

.76 

73 

55 

23.9 

636 

.08 

5. 

.4 

.20 

5 

1 

21.8 

1  la.  Geol.  Surv.,  Vol.  XIV,  p.  100,  1904. 

2  I.e. 


PHYSICAL   PROPERTIES  OF  CLAY  107 

Commenting  on  the  results  of  his  tests,  Zschokke  states  that  in 
very  plastic  clays  there  appears  to  be  a  slight  amount  of  elasticity,  so 
that  it  is  necessary  to  distinguish  between  elastic  and  permanent  changes 
of  form. 

The  reason  for  the  change  of  shape,  without  rupture  under  pressure, 
is  considered  to  be  as  follows: 

Given  two  moist  sand-grains  in  contact.  Since  these  are  not  plastic 
bodies,  they  have  but  little  absorptive  power  for  water,  and  are  therefore 
covered  by  but  a  thin  film  of  the  latter.  If  these  two  grains  are  slowly 
drawn  apart,  the  water  film  binding  them  together  is  soon  ruptured. 
On  the  other  hand  two  moist-clay  particles  will  be  surrounded  by  a 
thicker  layer  of  water  because  of  their  greater  attraction  for  it,  and 
these  two  can  be  separated  much  farther  without  rupturing  the  mass. 

Now  the  cylinder  of  moist  clay  can  be  considered  as  being  composed 
•of  a  great  number  of  clay  particles  surrounded  by  water,  and  the  smaller 
the  size,  and  greater  the  number  of  particles  of  clay  substance  in  the 
mass,  the  more  intimate  will  be  the  attraction  between  clay  and  water. 
With  an  increase  in  texture,  and  corresponding  decrease  in  water-content 
and  cohesion,  there  will  be  a  depression  of  the  tensile  strength.  While 
an  excess  of  water  may  depress  the  tensile  strength  of  the  soft  clay,  still 
very  plastic  clays,  although  showing  higher  cohesiveness  than  lean  ones, 
have  a  higher  strength,  which  Zschokke  believes  indicates  that  there 
is  an  intimate  relation,  of  either  chemical  or  physical  character,  between 
the  clay  substance  and  admixed  water. 

Grout,1  in  his  work  on  the  West  Virginia  clays,  arrived  at  conclusions 
somewhat  similar  to  those  of  Zschokke.2  He  considers  that  plasticity 
may  be  considered  as  involving  two  variable  factors,  viz.,  (1)  amount 
of  possible  flow  before  rupture,  and  (2)  resistance  to  flow  or  deformation. 
Plasticity,  he  says,  "  increases  in  direct  proportion  to  each  of  these  fac- 
tors, and  is  therefore  equal  to  the  product." 

He  measured  the  plasticity  by  carefully  mixing  and  tempering 
the  clay,  and  then  forced  it  into  a  thin-walled  metal  cylinder  three 
fourths  inch  in  diameter.  A  plunger  forced  the  clay  through  this  die, 
and  the  bar  of  clay  was  cut  into  two-inch  lengths. 

These  small  cylinders  were  placed  vertically  under  a  movable  plate 
and  pressure  applied,  the  amount  necessary  to  compress  it  one  half 
centimeter  being  taken  as  the  measure  of  resistance  to  flow  or  deforma- 
tion. 


1  W.  Va.  Geol.  Surv.,  Ill,  p.  40,  1906. 

2  I.e. 


108  CLAYS 

The  cylinder  was  then  further  compressed  until  the  appearance 
of  cracks  at  about  45  degrees  to  the  vertical  line,  and  this  was  considered 
the  point  of  fracture.  Vertical  cracks,  due  to  tension  as  the  cylinder 
"expanded;  were  disregarded,  and  an  irregular  swelling  of  the  cylinder 
under  pressure  was  an  indication  that  the  mass  was  not  uniform."  The 
amount  of  flow  was  measured  by  the  increase  in  area  of  the  head  of 
the  cylinder. 

The  resistance  to  flow  was  found  to  be  more  satisfactorily  measured 
by  use  of  a  Vicat  needle;  a  needle  of  seven  square  mm.  (J  in.)  was  used, 
and  weight  determined  which  was  necessary  to  cause  the  needle  to  sink 
three  centimeters  in  \  min. 

Tests  of  dry  clay. — Of  the  dry  methods,  the  tensile-strength  test 
is  the  best  known.  It  is  made  by  molding  the  wet  clay  into  briquettes, 
and  testing  the  tensile  strength  of  these  when  dry,  this  strength  being 
expressed  in  Ibs.  per  sq.  in.  The  objection  to  this  method  is  the  assump- 
tion that  the  plasticity  of  a  clay  stands  in  direct  relation  to  its  tensile 
strength,  which  is  incorrect. 

Bischof  x  suggested  using  a  set  of  mixtures  of  a  standard  clay  with 
varying  amounts  of  sand.  Each  of  these  is  rubbed  with  the  fingers,  and 
the  amount  of  dust  that  can  be  rubbed  off  is  noted.  The  clay  to  be 
tested  is  similarly  rubbed,  and  rated  with  the  one  of  the  standard  series 
which  has  lost  a  similar  amount  by  rubbing.  The  method  is  crude  and 
inaccurate. 

Texture 

Definition. — By  the  texture  of  a  clay  is  meant  its  size  of  grain  or 
fineness,  and  since  this  exerts  an  important  influence  on  the  physical 
properties,  such  as  plasticity,  shrinkage,  porosity,  fusibility,  etc.,  it 
should  receive  more  than  passing  consideration.  Many  clays  contain  sand- 
grains  of  sufficient  size  to  be  visible  to  the  naked  eye,  but  the  majority 
of  clay  particles  are  too  small  to  be  seen  without  the  aid  of  a  microscope, 
and  are  therefore  so  small  that  it  becomes  impossible  to  separate  them 
with  sieves.  In  testing  the  texture  of  a  clay,  it  is  perhaps  of  sufficient 
importance  for  practical  purposes  to  determine  the  per  cent  of  any 
sample  that  will  pass  through  a  sieve  of  100  or  150  meshes  to  the  inch, 
since,  in  the  preparation  of  clays  for  the  market  by  the  washing  process, 
they  are  not  required  to  pass  through  a  screen  any  finer  than  the  one 
above  mentioned. 

Mechanical  analysis. — If  it  is  desired  to  measure  the  size  of  all  the 
grains  found  in  the  clay,  some  more  delicate  method  of  separation  becomes 

1  Die  leuerfesten  Thone,  p.  88. 


PHYSICAL  PROPERTIES  OF  CLAY  109 

necessary,  and  in  order  to  do  this  it  is  essential  that  the  mass  of  clay 
should  be  first  thoroughly  disintegrated  and  the  grains  separated  from 
each  other.  This  is  best  done  by  shaking  the  clay  for  a  long  time  in 
water.1  For  this  purpose  the  bottles  used  in  sterilizing  milk  for  infants 
are  very  convenient.  Twenty  grams  of  clay  are  weighed  out  and  washed 
into  such  a  bottle  and  the  latter  about  half  filled  with  distilled  water. 
The  bottle  is  closed  with  a  rubber  stopper  and  put  into  a  shaking-machine. 
A  convenient  form  consists  of  a  box  with  compartments  for  holding 
four  tiers  of  bottles  lying  on  their  sides,  allowing  four  bottles  in  each 
compartment.  This  box  is  supported  by  chains,  attached  to  the  corners, 
hanging  from  brackets  above.  It  is  fastened  by  rubber  bands  to  the 
table  below,  to  steady  it,  and  a  guide-rod  is  fastened  to  the  bottom, 
which  works  between  two  uprights  to  give  a  true  lateral  motion  to  the 
box.  The  box  is  then  moved  rapidly  back  and  forth  by  a  crank,  with  a 
throw  of  about  5  inches,  at  a  rate  of  about  170  revolutions  per  minute. 
This  gives  a  very  good  motion  to  the  liquids  in  the  bottles  and  keeps 
the  clay  constantly  agitated.  Motion  may  be  imparted  to  the  shaker 
by  a  water-motor  or  other  suitable  power.  The  shaking  is  continued 
for  from  one  to  two  days,  according  to  the  nature  of  the  sample,  the 
heavier  clays  requiring  the  longer  time. 

When  shaking  is  stopped,  the  contents  of  the  bottles  are  washed 
into  beakers,  and  the  sediment,  which  quickly  subsides,  is  examined 
with  the  microscope.  If  the  disintegration  is  not  complete,  a  small 
amount  of  pestling  with  the  rubber-tipped  pestle  will  finish  it.  Usually 
sandy  clays  are  very  thoroughly  disintegrated  after  being  shaken  a  day, 
while  clay  soils  frequently  require  pestling  after  having  been  shaken 
for  two  days. 

When  clean,  the  grains  should  show  sharp  outlines  under  the  micro- 
scope, being  as  a  rule  quite  transparent.  Adhering  particles  make 
them  appear  rounded  and  more  or  less  deeply  colored  and  the  outlines 
indistinct.  When  pestling  alone  is  resorted  to  for  the  disintegration  of 
the  material,  it  may  require  from  fifteen  minutes  to  an  hour  or  more, 
depending  upon  the  nature  of  the  sample. 

1  U.  S.  Dept.  of  Agric.,  Bur.  of  Soils,  Bull.  4,  p.  9,  1896. 


110  CLAYS 


Methods  of  Separation 

Beaker  method. — This  method  suggested  by  Whitney  is  simple,. 
but  somewhat  inconvenient  on  account  of  the  large  amount  of  water 
required.  Its  operation  is  as  follows:  l 

"The  thoroughly  disintegrated  clay  is  transferred  to  a  3-inch  beaker, 
which  we  may  call  S.  This  is  filled  with  water  and  thoroughly  stirred. 
It  is  then  allowed  to  settle  until  all  solid  particles  larger  than  0.05  mm. 
have  subsided.  This  is  determined  by  taking  a  sample  of  the  turbid 
liquid  from  near  the  bottom  of  the  beaker  by  lowering  a  small  tube, 
with  the  top  closed  by  the  finger,  to  a  point  just  above  the  sediment, 
then  removing  the  finger  for  an  instant  and  letting  the  liquid  enter  the 
tube,  closing  the  tube  with  the  finger  again  and  withdrawing  the  sample. 
A  drop  of  this  is  placed  upon  a  microscope  slide,  a  cover-glass  placed 
over  it,  and  the  particles  examined  by  a  good  microscope  containing 
an  eyepiece  micrometer.  It  is  convenient  to  use  a  1-inch  eyepiece  and  a 
three-fourths  and  one-fifth  inch  objective. 

"When  the  particles  larger  than  0.05  have  subsided,  the  turbid 
liquid  is  carefully  decanted  into  a  larger  beaker,  M.  This  turbid 
liquid  contains  silt,  fine  silt,  and  clay,  but  no  sand  if  the  separation 
has  been  properly  timed.  The  sediment  in  S  consists  of  sand,  containing, 
still  some  silt,  fine  silt,  and  clay.  This  is  stirred  up  with  water  and 
again  allowed  to  settle  until  all  the  grains  of  sand  have  subsided,  when 
the  turbid  liquid  is  again  decanted  into  M.  This  operation  is  continued 
until  an  examination  of  the  sediment  in  B  shows  that  all  particles  smaller 
than  0.05  mm.  have  been  removed.  The  contents  of  this  beaker  B  are 
then  washed  into  a  small  porcelain  dish  and  evaporated  to  dryness  on 
the  water-bath.  When  dry  this  sand  may  be  gently  ignited  to  burn 
off  the  organic  matter,  and  when  cool  it  is  sifted  through  a  series  of 
sieves  which  will  be  described  further  on. 

"It  is  often  convenient  in  separating  the  silt,  fine  silt,  and  clay  from 
the  sand  to  decant  before  the  last  portions  of  sand  have  settled.  This 
hastens  the  operation  of  separating  the  fine  and  the  coarse  material, 
especially  where  there  is  a  large  mass  of  sand  and  but  little  fine  material 
to  be  removed.  In  this  case,  the  turbid  liquid  which  is  decanted  is 
put  into  a  separate  beaker,  and  the  sand  which  has  been  poured  off  is 
recovered  by  a  further  decantation,  and  when  free  from  all  fine  material 
it  is  added  to  the  sand  in  the  porcelain  dish  while  the  latter  is  evaporating 
to  dryness.  The  turbid  liquid  in  the  breaker  M.  is  thoroughly  stirred 

1  U.  S.  Dept.  Agric.,  Bur.  of  Soils,  Bull.  4,  p.  10,  1896. 


.  PHYSICAL  PROPERTIES  OF  CLAY  111 

and  allowed  to  settle  until  a  drop  taken  from  near  the  bottom  of  the 
the  beaker  contains  no  solid  particles  larger  than  0.01  mm.,  equal  to 
two  spaces  of  the  eyepiece  micrometer  using  the  -£-inch  objective.  The 
turbid  liquid,  containing  only  fine  silt  and  clay  in  suspension,  is  then 
carefully  decanted  into  another  beaker,  P.  The  sediment  remaining 
in  M  is  again  stirred  up  with  water  and  allowed  to  settle,  and  decanted 
as  before.  This  operation  is  continued  until  all  particles  smaller  than 
0.01  mm.  have  been  washed  out  of  the  sediment  in  the  beaker.  Care 
must  be  taken  in  pouring  off  the  turbid  liquid  that  none  of  the  silt  goes 
over,  or  if  it  does  it  must  be  recovered  and  added  to  that  in  beaker  M 
at  some  later  stage  of  the  operation.  The  sediment  remaining  in  beaker 
M  should  contain  nothing  larger  than  0.05  nor  smaller  than  0.01,  if 
the  separation  has  been  carefully  and  completely  made.  This  is 
washed  into  a  platinum  dish,  evaporated  to  dry  ness  on  the  water- 
bath,  ignited  at  a  low  red  heat,  cooled  in  a  desiccator,  and  finally 
weighed. 

"  The  sediment  in  beaker  P  containing  fine  silt  and  clay  is  stirred 
up  with  water  and  allowed  to  settle  until  everything  larger  than  0.005 
mm.  has  subsided,  as  determined  by  a  microscopic  examination  as  before. 
The  turbid  liquid,  containing  only  '  clay  '  or  material  finer  than  0.005 
mm.  equal  to  one  space  of  the  micrometer,  is  then  decanted  into  a  larger 
beaker,  C,  of  1  or  2  liters  capacity,  and  the  sediment  in  P  repeatedly 
washed  until  all  of  the  clay  has  been  removed.  When  this  has  been 
accomplished,  the  sediment  is  washed  into  a  platinum  dish,  evaporated 
to  dryness,  ignited,  and  weighed. 

"  The  clay  water  usually  amounts  to  a  number  of  liters,  and  to  prevent 
it  accumulating  to  any  great  extent  it  is  the  practice  in  this  Division  to 
measure  it  in  a  liter  flask  and  take  100  cc.  from  each  liter  to  evaporate 
to  dryness.  The  remainder  of  the  clay  solution  is  thrown  away.  When 
the  liter  flask  is  full  to  the  mark  with  the  clay  solution,  care  must  be 
taken  to  thoroughly  mix  it  before  taking  out  the  tenth  part  to  be  evapo- 
rated to  dryness.  The  successive  100  cc.  of  clay  water  are  poured  into 
a  beaker  and  evaporated  in  a  platinum  dish  as  rapidly  as  possible.  When 
this  clay  water  has  been  evaporated  to  dryness,  the  sediment  is  ignited 
and  weighed  and  the  weight  multiplied  by  ten  to  give  the  total  amount 
of  fine  material  in  the  original  sample. 

11  In  the  course  of  the  analysis,  several  of  these  grades  may  be  separated 
at  once,  to  facilitate  the  operation,  by  the  use  of  additional  beakers. 
It  is  best  to  transfer  material  into  smaller  beakers  as  the  quantity  becomes 
less  in  being  freed  from  the  finer  particles,  as  this  materially  hastens  the 
time  required  for  the  material  to  subside. 


112  CLAYS 

"  The  sand  which  was  separated  in  the  beginning  of  the  operation  and 
dried  and  ignited  in  the  porcelain  dish  is  sifted  through  a  series  of  sieves 
of  the  following  dimensions:  Three  round  brass  sieves  4  inches  in 
diameter  are  used,  which  fit  into  each  other  and  into  a  cup  at  the  bottom. 
The  top  sieve  has  circular  holes  2  mm.  in  diameter,  the  second  has  similar 
holes  1  mm.  in  diameter,  and  the  third  has  holes  0.5  mm.  in  diameter. 
These  grades  are  sifted  in  a  very  short  time. 

"  The  material  which  passes  through  the  lower  sieve  is  then  sifted 
through  two  grades  of  bolting-cloth — Nos.  5  and  13 — having  square 
holes  approximately  0.25  and  0.1  mm.  in  linear  dimensions.  This  sifting 
requires  quite  a  long  time,  on  account  of  the  fineness  of  the  spaces  through 
which  the  particles  have  to  pass.  It  can  conveniently  be  done  upon 
the  shaker  which  is  used  for  the  disintegration  of  the  original  sample. 
The  two  pieces  of  bolting-cloth  can  be  fitted  into  conveniently  arranged 
brass  rings,  and  the  samples  should  be  shaken  for  an  hour  or  two  on  this 
shaker. 

11  Each  of  these  grades  of  sand  are  weighed  without  previous  drying, 
as  the  amount  of  hygroscopic  moisture  is  usually  inappreciable. 

"  The  operation  of"  mechanical  analysis  is  frequently  made  tedious 
and  sometimes  impossible  by  flocculation.  If  any  tendency  to  this  is 
discovered,  vigorous  stirring  should  be  resorted  to,  arid  this  can  best 
be  done  with  one  of  the  improved  forms  of  egg-beaters  found  in  the 
market.  A  small  trace  of  ammonia  also  assists  in  overcoming  this 
tendency  to  flocculation,  but  it  should  be  added  very  cautiously,  as  an 
excess  of  ammonia  will  cause  many  soils  to  flocculate.  If  the  sediments 
are  left  standing  for  a  length  of  time,  flocculation  is  liable  to  occur,  and 
it  is  very  important  that  the  work  should  be  pushed  along  as  rapidly 
as  possible.  The  operator  will  find  by  experience  that  while  waiting 
for  one  sediment  to  subside  he  may  be  decanting  into  extra  beakers, 
which  in  time  may  be  added  to  the  proper  beaker. 

"  The  water  used  in  the  mechanical  analysis  should  be  distilled,  if 
possible,  but  clear  river,  well,  or  hydrant  water  may  be  used.  In  case 
distilled  water  is  not  available,  the  solid  matter  in  suspension  or  in 
solution  in  the  water  used  should  be  determined  by  evaporating  500  cc. 
of  the  water  to  dryness,  and  igniting  and  weighing  the  residue.  Allowance 
should  then  be  made  for  this  residue  in  the  clay  determination. 

"  Eight  or  ten  samples  can  be  started  at  once  and  can  be  pushed  through 
about  as  readily  as  a  single  sample.  It  is  not  advisable,  however,  to 
attempt  to  carry  on  more  than  this  number,  because  the  proper  attention 
cannot  be  given  to  the  beakers.  A  fresh  set  of  samples  may  be  started 
on  the  shaker,  however,  a  day  or  two  before  the  last  set  is  finished. 


PHYSICAL  PROPERTIES  OF  CLAY 


113 


It  requires  from  six  to  ten  days  to  complete  the  analyses  of  a  set  of 
samples,  if  close  attention  is^given  to  the  decantations. " 

Schoene  method. — A  second  method  consists  in  separating  the 
pebbles  and  coarse-sand  particles  cut  of  the  disintegrated  clay  by  means 
of  sieves,  and  then  placing  the  finer  portion  in  a  tube  where  it  is  exposed 
to  an  upward  current  of  water. 
Since  the  carrying  power  of  the 
current  will  increase  with  its  veloc- 
ity, a  current  of  water  rising  very 
slowly  in  the  tube  will  carry  off 
only  the  finest  particles,  while  the 
heavier  ones  remain  behind.  If 
the  velocity  of  the  current  be  kept 
at  this  speed,  it  will  finally  become 
clear  when  all  the  finest  particles 
are  carried  off. 

A  form  of  apparatus  used  for 
this  purpose  is  the  Schoene  elutriator 
shown  in  Fig.  20. 

The  apparatus  consists  of  the 
separating  funnel  A,  which  at  the 
bottom  ends  is  a  bent  tube,  and  is 
connected  at  the  top  with  a  narrow 
tube  1  meter  long.  This  latter  is 
Z-shaped  and  has  an  opening  at 
L,  ]  .5  mm.  in  diameter.  The  grains 
of  the  clay  to  be  separated  are  first 
disintegrated  by  boiling  and  then 
placed  in  the  funnel  A.  Water  is 
then  run  in  from  the  reservoir  D  FIG.  20.— Schoene's  apparatus  for  me- 
and  the  supply  regulated  by  the  chanical  analysis  of  clay, 

stopcock  E,  so  that  there  is  always  a  definite  velocity  in  the  funnel  A. 
The  rapidity  of  flow  depends  on  the  amount  of  water  entering  the  funnel 
per  second.  Knowing  the  amount  of  water  and  the  cross-section  of 
A,  the  velocity  is  equal  to  the  quantity  divided  by  the  cross-section. 
The  quantity  is  measured  by  allowing  it  to  run  into  a  measuring-vessel 
for  a  definite  length  of  time,  care  being  taken  that  the  level  of  the  water 
in  k  remains  constant.  In  this  way  the  flow  per  second  can  be  calculated. 

The  velocity  of  the  flow  can  be  told  by  the  height  to  \vhich  the  water 
backs  up  in  the  tube  k.  This  has  to  be  determined  in  calibrating  the 
instrument. 


114 


CLAYS 


To  every  velocity  there  corresponds  a  size  of  grain  determined  by 
calculations,  and  five  sizes  are  made,  as  fellows: 

1.  Clay  substance,  including  particles  removed  by  a  flow  of  0.18  mm. 
per  second.     Maximum  diameter  0.01  mm. 

2.  Silt,  including  grains  removed  by  a  flow  of  0.70  mm.  per  second. 
Maximum  diameter  0.025. 

3.  Dust-sand,  including  particles  removed  by  a  flow  of  1.5  mm.  per 
second.     Maximum  size  0.04  mm. 

4.  Residue  remaining  in  funnel,  called  fine  sand.     Diameter  0.04  to 
0.2  mm. 

5.  Coarse  sand,  everything  larger  than  0.2  mm. 

This  form  of  apparatus  is  much  used  in  Germany,  and  but  little 
in  the  United  States.  An  objection  which  has  been  urged  against  it  is 
that,  on  account  of  the  funnel-shaped  character  of  the  vessel  A,  counter- 
currents  are  set  up,  which  interfere  with  accurate  results. 


FIG.  21. — Hilgard's  apparatus  for  making  mechanical  analyses. 

Hilgard's  elutriator. — E.  W.  Hilgard  devised  the  form  of  apparatus 
shown  in  Fig.  21  for  overcoming  the  defects  of  Schoene's  separator. 
It  is  known  as  Hilgard's  Churn  Elutriator.  It  consists  of  an  upright 
glass  cylinder,  300  mm.  in  height  and  45  mm.  in  diameter;  this  cylinder 
is  united  at  its  lower  end  to  a  brass  cup-shaped  funnel,  crossed  by  a 
horizontal  axis  furnished  with  four  wings;  this  churn  is  separated  from 
the  cylinder  by  a  wire  screen  with  meshes  0.8  mm.  in  diameter.  The 
churn  is  worked  by  any  convenient  motor-power;  about  500  revolutions 
per  minute  is  the  speed  required  when  separating  the  two  finest  groups 
of  particles,  but  for  the  other  separations  a  smaller  velocity  will  suffice. 


PHYSICAL   PROPERTIES    OF  CLAY  115 

The  lower  end  of  the  brass  funnel  is  fixed  into  a  conical  test-glass,  which 
is  in  connection  with  the  water-supply.  The  water  is  supplied  from  a 
reservoir  maintained  at  a  constant  level.  The  lever  opening  the  water- 
tap  moves  over  a  graduated  arc,  on  which  are  marked  the  positions  of 
the  lever  which  yield  supplies  of  water,  giving  the  required  velocities  in 
the  glass  cylinder. 

The  apparatus  being  half  filled  with  water  and  the  churn  in  motion, 
the  sediment  is  introduced,  and  the  water-current  adjusted  to  the  low- 
est velocity,  0.25  mm.  per  second;  this  current  is  continued  till  the 
water  ceases  to  remove  any  more  matter.  The  operation  requires 
many  hours  for  its  completion.  The  object  of  the  churn  is  to  break 
up  the  aggregations  of  fine  particles  which  are  very  apt  to  form.  Should 
any  be  seen  on  the  sides  of  the  cylinder,  the  apparatus  must  be  stopped, 
and  the  flocks  detached  with  a  feather.  The  water  leaving  the  cylinder 
is  conducted  by  a  tube  nearly  to  the  bottom  of  a  tall,  wide  vessel,  from 
the  top  of  which  the  water  runs  to  waste.  The  receiving  vessel  being 
much  wider  than  the  separating  cylinder,  the  upward  current  of  water 
in  it  is  too  slow  for  any  of  the  solid  matter  carried  into  it  to  escape. 

When  no  more  particles  are  removed  by  the  current  moving  0.25  mm. 
per  second,  the  regulator  is  changed,  and  the  velocity  of  the  current 
increased  to  0.5  mm.  per  second.  When  the  second  group  of  particles 
has  been  in  this  way  removed,  the  velocity  of  the  current  is  again  doubled, 
and  this  mode  of  proceeding  is  continued  till  the  last  separation,  with 
a  velocity  of  64  mm.  per  second,  is  completed.  With  velocities  above 
4  mm.  per  second,  the  churn  may  be  dispensed  with.  The  work  gets 
more  rapid  as  the  higher  velocities  are  reached.  When  the  apparatus 
is  in  action  day  and  night,  the  separations  will  be  completed  in  three 
or  four  days.  Soft,  filtered  water  should  be  used  in  all  the  operations. 

A  most  serious  objection  to  the  three  methods  just  described  is  the 
time  required  for  making  an  analysis,  and  the  quantity  of  water  con- 
sumed. 

Centrifugal  separator. — The  most  satisfactory  method  is  that  known 
as  the  centrifugal  method.  The  apparatus  (Fig.  22)  used  consists 
of  a  fan-motor  1  placed  with  the  armature  shaft  in  a  vertical  position. 
This  carries  a  framework  with  eight  test-tube  holders,  trunnioned 
so  that  they  can  swing  outward  and  upwards  as  the  frame  revolves. 

The  disintegrated  sample  in  suspension  in  water  is  placed  in  these 
tubes,  and  twirled  at  a  high  speed  for  several  minutes.  As  a  result 
of  this,  all  particles  except  the  finest  clay  grains  are  thrown  to  the  bot- 

1  For  complete  description,  see  Bulletin  No.  64,  Bureau  of  Soils,  Dept.  of  Agri- 
culture, Washington,  1900. 


116 


CLAYS 


torn  of  the  tube  by  centrifugal  force.  These  are  decanted  off,  the  tubes 
refilled  with  water,  and  the  sediment  again  stirred  up.  A  second  twirling 
of  the  tubes,  either  at  a  lower  speed  or  for  a  shorter  period,  precipitates 
everything  except  the  fine  silt,  which  is  then  also  decanted  off.  The 
subsequent  sizes  are  then  separated  from  each  other  partly  by  settling 
and  partly  by  sieves. 


FIG.  22. — Centrifugal  separator  for  mechanical  analysis.    (Photo  loaned  by 

Bureau  of  Soils.) 

The  different  sizes  which  can  be  so  separated  and  their  dimensions 
are  shown  in  the  table  below: 


TABLE  SHOWING  SIZE  OF  GRAINS  OF  SAND,  SILT,  AND  CLAY 

Size  of  diameters. 
Conventional  name.  Inches. 

1.  Gravel 1/12  -1/25 

2.  Coarse  sand 1/25  -1/50 

3.  Medium  sand 1/50  -1/100 

4.  Fine  sand 1/100-1/250 

5.  Very  fine  sand 1/250-1/500 

6.  Silt 1/500-1/2500 

7.  Fine  silt 1/2500-1/5000 

8.  Clay 1/5000-1/25000 

If  a  raw  clay  is  examined  under  the  microscope 
to  be  composed  of  a  number  of  different-sized  grains. 


Millimeters. 

2-1 

1-0.5 
0.5-0.25 
0.25-0.1 
0.1-0.05 
0.05-0.01 
0.10-0.005 
0.005-0.001 

it  is  usually  seen 
These  may  show 


PHYSICAL  PROPERTIES  OF  CLAY 


117 


a  wide  range  of  sizes  as  given  in  Fig.  23,  which  represents  a  gritty  clay 
from  the  Cape  May  formation  of  New  Jersey.  In  other  clays,  such 
as  those  of  the  Alloway  formation  in  the  same  State,  there  is  often 


0° 


•m 

•"*  —  *\.        ** 

\  •« 

°o 

oO        °^° 

a 


o^    ° 


o^1 


FIG.  23.— Drawing  showing  particles  of  a  Cape  May  clay,  enlarged  362  diameters. 
(After  Ries,  N.  J.  Geol.  Surv.,  Fin.  Rept.,  VI,  p.  109,  1904.) 

less  variation  in  the  size  of  the  grains  (Fig.  24),  the  grains  in  the  latter 
being  bunched  together  more  than  in  the  former.  Fig.  25  represents 
several  grains  of  sand  from  a  sample  of  Clay  Marl  I,  which  have  been 
separated  by  the  mechanical  analysis  and  enlarged  115  diameters; 
they  consist  of  quartz  (Q),  mica  (M),  feldspar  (F),  and  lignite  (L), 
the  cloudiness  of  the  feldspar  being  due  to  partial  kaolinization. 

Relation  between  composition  and  texture. — Few  analyses  have 
been  published  showing  the  chemical  composition  of  the  different-sized 
grains  in  a  clay. 

Recently  Grimsley  and  Grout  have  analyzed  the  mechanical  sepa- 
rations of  16  samples  of  clay  with  the  following  results:1 

1  W.  Va.  Geol.,  Ill,  p.  61,  1906. 


118 


CLAYS 


Sizes  in  mm. 

00  to 
0.001 

0.001  to 
0.005 

0.005  to 
0.02 

0  .  02  to 
0.15 

0.15  up 

Silica   (SiO2)  .  .  . 

44  08 

54  54 

70  30 

81  16 

73  63 

Alumina   (A12O3)  

28  16 

23  00 

16  04 

9  76 

13  01 

Ferric  oxide  (Fe2O3) 

7  94 

5  91 

3  21 

2  13 

4  71 

Ferrous  oxide  (FeO) 

99 

99 

63 

40 

18 

Lime    (CaO)  .                  

"76 

82 

72 

31 

.47 

Magnesia   (MgO)  

1.36 

l76~2 

.80 

.39 

.48 

Potash   (K2O)  

3~05 

3.31 

2.14 

1.78 

.93 

Soda   (Na2O)    

00 

.29 

.45 

.56 

.00 

Moisture 

2  80 

1   10 

56 

~35 

.87 

Ignition,  loss  

10.86 

7.79 

4.33 

2.59 

4.40 

Titanic  oxide  (TiO2)  

.84 

1.12 

1.08 

.78 

.60 

/ 

p  ,  °8<* 

b 

go  3 

§>A  • 

°0o    0 

g°° 

tOo 

o    tfS? 

{700 

0     a  °n 

V?o^>Q         oQ&c^ 

0   o    o 

:o 

o 

s»* 

o 

o 


^ 

0 


FIG.  24.— Drawing  of  the  Alloway,  N.  J.,  clay,  enlarged  362  diameters.     (After  Ries, 
N.  J.  Geol.  Surv.,  Fin.  Kept.,  VI,  p.  110,  1904.) 

As  might  be  expected,  these  analyses  show  a  higher  percentage  of 
silica  in  the  coarser  grains,  still  the  increase  is  not  a  steady  one,  but 
none  of  the  other  ingredients  show  either  an  increase  or  decrease  from 


PHYSICAL   PROPERTIES  OF  CLAY 


119 


FIG.  25. — Drawing  of  sand-grains  in  a  New  Jersey  clay  marl,  enlarged  115  diam- 
eters. M,  mica;  Q,  quartz;  F,  feldspar;  L,  lignite.  (After  Ries,  N.  J.  Geol. 
Surv.,  Fin.  Rept.,  VI,  p.  Ill,  1904.) 


FIG.  26. — Drawing  showing  bunches   of  kaolinite  (?)  plates  in  a  ball-clay  from 
Edr-ar,  Fla.,  enlarged  362  diameters.     (After  Ries,  Md.  Geol.  Surv.,  IV.) 


120 


CLAYS 


coarse  to  fine.  The  maxima  are  in  each  case  underscored.  The  appre- 
ciable titanium  percentage  in  even  the  coarser  grains  is  of  interest, 
although  it  is  not  known  in  what  form  the  titanium  occurs  therein. 

Tensile  Strength 

Definition. — The  tensile  strength  of  a  clay  is  the  resistance  which 
it  offers  to  rupture  or  being  pulled  apart  when  air-dried. 

Practical  bearing.. — The  tensile  strength  is  an  important  property, 
and  has  a  practical  bearing  on  problems  connected  with  the  handling 
molding,  and  drying  of  the  ware,  since  a  high  strength  enables  the  clay 
to  withstand  the  shocks  and  strains  of  handling.  Through  it,  also, 
the  clay  is  able  to  carry  a  large  quantity  of  non-plastic  material,  such  as 
flint  or  feldspar,  ground  bricks,  etc. 

Relation  to  plasticity. — Although  it  was  formerly  believed  by  many 
that  tensile  strength  and  plasticity  were  closely  related,  this  view  is 
no  longer  generally  accepted.  High  tensile  strength  and  high  plas- 
ticity often  go  together,  but  a  clay  low  in  tensile  strength  may  have 
high  plasticity  and  vice  versa. 

Measurement  of  tensile  strength. — The  tensile  strength  is  measured 
by  molding  the  thoroughly  kneaded  clay  into  briquettes,  of  the  form 

and  dimensions  shown  in  Fig.  27,  and, 
when  thoroughly  air-dried,  pulling  them 
apart  in  a  suitable  testing-machine.  The 
cross-section  of  the  briquettes  when 
molded  is  1  square  inch,  and,  after  being 
formed,  they  are  allowed  to  dry  first 
in  the  air  and  then  in  a  hot-air  bath 
at  a  temperature  of  100°  C.  (212°  F.). 
When  thus  thoroughly  dried  the  briquette 
is  placed  in  a  machine,  in  which  its  two 
ends  are  held  in  a  pair  of  brass  clips,  and 
is  subjected  to  an  increasing  tension  until 
it  breaks  into  two.  The  type  of  machine 
used  is  of  either  type  shown  in  Figs.  28 
and  29.  Theoretically  the  briquette 
should  break  at  its  smallest  cross-sec- 
tion with  a  smooth,  straight  fracture, 
and  when  this  does  not  occur  it  is  due 
FIG.  27. — Outline  and  dimensions  either  to  a  flaw  in  the  briquette  or  because 
of  a  briquette  for  testing  the  the  clipg  tend  to  cut  into  the  ciay  In 


tensile  strength  of  a  clay. 


such  event   the   briquette  breaks   across 


one  end,  and  to  prevent  this  it  is  necessary  to  put  some  soft  material, 


PHYSICAL  PROPERTIES   OF  CLAY 


121 


such  as  asbestos,  pasteboard,  or  rubber  between  the  inner  surface  of 
the  clip  jaws  and  the  sides  of  the  briquette.  If  the  briquettes  are 
molded  and  dried  with  care,  the  variation  in  the  breaking  strength  of 
the  individual  briquettes  should  not  vary  more  than  15  or  20  per  cent, 
but  with  some  very  plastic  clays  it  is  extremely  difficult  to  keep  the 
variation  within  these  limits. 


FIG.  28. — Richie"  tensile-strength  machine. 

Great  care  has  to  be  exercised  in  filling  the  briquette  molds,  in  order 
to  prevent  flaws  in  the  piece,  and  the  best  method  consists  in  cutting 
a  lump  of  the  tempered  clay  of  approximately  the  shape  and  size  of 
the  mold,  and  then  pounding  it  in  from  both  sides  with  the  hands. 

Wheeler  1  advocates  filling  the  mold  by  pressing  in  separate  small 
pieces  of  wet  clay  with  the  fingers,  the  object  of  this  being  to  avoid 
air-bubbles  and  prevent  laminations  in  the  briquette;  but  some  have 
obected  to  this,  on  the  ground  that  it  is  difficult  to  make  the  separate 
pieces  of  clay  amalgamate. 

Since  the  briquettes  of  any  one  clay  will  always  show  more  or  less 
variation,  at  least  10  or  12  should  be  tested  in  order  to  get  a  fair  aver- 
age. The  author's  experience  has  shown  that  the  greatest  variation 
usually  appears  in  clays  of  high  tensile  strength,  in  which  the  fracture 
nearly  always  occurred  in  the  head,  indicating  that  the  briquettes  broke 
before  the  limit  of  their  strength  was  reached.  The  tensile  strength 
of  clay  briquettes  is  expressed  in  pounds  per  square  inch;  but,  sirce 

1  Mo.  Geol.  Surv.,  Vol.  XI,  p.  111. 


122 


CLAYS 


the  briquette  shrinks  in  drying,  the  strength  actually  obtained  in  test- 
ing will  be  less  than  that  for  a  square  inch,  and  the  result  must  be 
increased  in  proportion  to  the  amount  the  brick  has  shrunk. 


FIG.  29. — Fairbanks  tensile-strength  machine.  N,  clips  for  holding  briquettes; 
P,  screw  for  applying  strain  to  balance-lever  C;  F,  bucket  to  hold  shot 
fed  in  through  /  from  the  hopper  K\  J ,  automatic  cut-off. 

Clays  vary  widely  in  their  tensile  strength,  ranging  from  but  a  few 
pounds  up  to  over  400,  and  even  in  clays  of  the  same  class  a  wide  vari- 
ation is  not  uncommon,  as  the  following  approximate  figures  will  show: 


Kaolins 

Fire-clays.  . . . 
Brick-clays. .  . 
Pottery-clays. 


Minimum.  Maximum. 

20  60 

0  (Flint-clays)  150 
50  300 

50  250 


Wheeler 1  in  testing  135  Missouri  clays  found  that  their  tensile 
strength  ranged  from  an  average  of  8  to  380  Ibs.  per  square  inch,  dis- 
tributed among  the  several  kinds  as  follows: 


Kind. 
Flint-clays  ...       , 

Range. 
,  8  to     50 

Average 
20 

Kaolins 

12  to    20 

20 

Fire  clays  and  pottery-clays 

50  to  284 

150 

Shales     .                  

87  to  192 

120 

Gumbo  

275  to  410 

340 

Loess              .    .               

97  to  354 

150 

1  Mo.  Geol.  Surv.,  XI,  p.  111. 


PHYSICAL  PROPERTIES  OF  CLAY  123 

Beyer  and  Williams  1  give  a  range  of  from  46  to  319  Ibs.  per  square 
inch  for  the  Iowa  clays. 

The  range  in  strength  determined  by  the  writer  for  the  Texas  clays 
was  as  follows: 

Fire  clays 46  to  277 

Stoneware  clays 66  to  320 

Calcareous  clays 119  to  366 

Sandy  brick  clays 77  to  455 

Semi-refractory  brick  clays 161  to  329 

Red-  or  brown-burning  brick  clays 74  to  487 

while  in  the  New  Jersey  clays2  the  extremes  were  20  and  453  Ibs.  per 
square  inch. 

When  any  series  of  clays  is  tested,  it  is  found  that  both  the  very  sandy 
ones  and  very  fine-grained  ones  often  have  a  low  tensile  strength,  although 
there  are  marked  exceptions  to  both  these  cases. 

Cause  of  tensile  strength. — In  order  to  get  satisfactory  and  reliable 
results,  great  care  is  necessary  in  molding  and  drying  the  briquettes,  it 
being  claimed  by  some  that  fine-grained  clays  will  show  an  abnormally 
low  strength  unless  dried  very  slowly. 

Experiments  by  Orton  3  seem  to  bear  out  this  fact.  Five  series  of 
the  same  clay  were  tested  by  him  as  follows: 

Average 

Series.  Rate  of  drying.  tensile  strength, 

Ibs.  per  sq.  in. 

1 Quickest,  severest  drying 182 . 49 

2 Somewhat  slower 178 . 17 

3 Still  slower 176.13 

4 Very  slow  indeed 204 . 80 

5 Artificial  conditions 205 . 53 

The  fifth  series  was  placed  in  a  tightly  closed  jar  with  calcium  chloride. 

With  such  a  variation  existing  in  the  tensile  strength  of  clays,  it 
becomes  a  matter  of  importance  to  know  the  cause  of  this  variation. 
It  is  a  well-known  fact  that  all  clays  shrink  in  drying,  and  that  this 
shrinkage  is  accompanied  by  a  drawing  together  of  the  particles.  Indeed, 
some  clays  shrink  to  such  a  hard  mass  as  to  suggest  a  close  interlocking 
of  the  grains,  which,  it  seems  to  the  writer,  may  be  the  explanation  of 
the  tensile  strength  shown;  that  is  to  say,  those  clays  in  which  the  inter- 

1  la.  Geol.  Surv.,  XIV,  p.  83,  1904. 

2  N.  J.  Geol.  Surv.,  Final  Report,  Vol.  VI,  p.  85,  1904. 
» Trans.  Amer.  Cer.  Soc.,  Vol.  Ill,  p.  202,  1901. 


124 


CLAYS 


locking  of  the  particles  is  the  tightest  will  show  the  highest  tensile  strengtn 
and  vice  versa.  If  this  is  true  it  becomes  necessary  to  determine,  if 
possible,  what  arrangement  or  size  of  particles  produces  the  tightest  and 
strongest  structure. 

E.  Orton,  Jr.,1  attempted  to  determine  the  effect  of  the  fineness  of  grain 
on  the  tensile  strength  of  clays  by  taking  a  very  fine-grained  clay  and 
mixing  different  sizes  of  sands  with  it,  the  sand  being  obtained  by  grinding 
and  screening  vitrified  bricks.  His  conclusions  were  "  (1)  that  the 
tensile  strength  of  mixtures  of  a  plastic  ball-clay  with  equal  quantities  of 
non-plastic  sands  will  vary  inversely  with  the  diameter  of  the  grains  of 


90 


80  70  60  50  40 

Diameter  of  grains  in  terras  of  the  largest. 


30  20  10 

Largest  size  =100 


FIG.  30. — Curve  showing  relation  between  fineness  of  grain  of  non-plastic  material 
and  tensile  strength  of  clay  mixtures.   (After  Orton,  Trans.  Amer.  Cer.  Soc.,  III.) 

the  sand  from  grains  of  0.04  inch  down  to  the  finest  sizes  obtainable. 
(2)  That  the  non-plastic  ingredients  of  clay  influence  its  tensile  strength 
inversely  as  the  diameter  of  their  grains,  and  fine-grained  clays  will, 
other  things  being  equal,  possess  the  greatest  tensile  strength."  In 
other  words,  the  coarser  the  grains  of  sand  the  less  the  tensile  strength 
of  the  mixture  containing  them. 

The  results  of  these  tests  are  shown  graphically  in  Fig.  30. 

1  Transactions  American  Ceramic  Society,  Vol.  II,  p.  100,  and  Vol.  Ill,  p.  198. 


PHYSICAL  PROPERTIES  OF  CLAY 


125 


A  series  of  tests  on  natural  mixtures  of  varying  texture  were  under- 
taken by  the  writer  in  connection  with  a  study  of  the  New  Jersey  clays.1 
Five  samples  were  selected  at  random  as  follows: 

1.  A   very    plastic,   slightly   gritty,   dense,   red-burning    clay    from 
the  Alloway  formation,  with  an  average  tensile  strength  of  453  pounds 
per  square  inch. 

2.  A  Pleistocene  clay  of  gritty,  plastic  character,  but  not  as  dense  as 
the   previous  one.     Its  average  tensile  strength  was  297  pounds  per 
square  inch. 

3.  A  gritty,  plastic  clay  from  the  Cape  May  formation,  with  an  aver- 
age tensile  strength  of  289  pounds  per  square  inch. 

4.  A  Raritan  clay  of  black  color  and  sandy,  micaceous  character, 
with  an  average  tensile  strength  of  105  pounds  per  square  inch. 

5.  A  soft,  powdery,  washed  ball   clay  from  the   Raritan.     It  was 
plastic  to  the  feel,  with  very  little  grit,  and  a  tensile  strength  of  under 
20  pounds  per  square  inch. 

The  percentage  of  the  sizes  in  each  of  the  5  samples  is  shown  in  the 
following  table: 

MECHANICAL  ANALYSES  OF  SOME  NEW  JERSEY  CLAYS 


Conventional  names. 

I. 

Lab.  No. 
680. 

II 

Lab.  No. 
659. 

III. 

Lab.  No. 
645. 

IV- 

Lab.  No. 
615. 

V. 

Lab.  No. 
723. 

Clay  substance           .  . 

59.00% 

44.00% 

22.00% 

30  .  645% 

87  .  96% 

Fine  silt 

11.00 

7.11 

5.66 

14.21 

6.95 

Silt  and  fine  sand 

14.70 

24.35 

26.55 

5.585 

3.00 

Medium  sand               ... 

3.50 

7.80 

11  45 

6  400 

1.00 

gancl                             

11.40 

16.35 

33  44 

42  950 

99.60 

99.61 

99.10 

99.790 

98.91 

These  figures  seem  to  throw  some  light  on  the  relation  of  the  texture 
to  the  tensile  strength,  but,  while  highly  suggestive,  are  not  to  be  taken 
as  final.  The  results  of  these  tests  are  also  shown  graphically  in  the 
table  (Fig.  31),  in  which  the  horizontal  lines  represent  percentages.  Of 
the  6  columns,  the  first  5  represent  the  grain  sizes  and  the  sixth  the 
tensile  strength. 

Taking  No.  5  of  the  above  table  of  analyses  we  find  that  it  contains 
87.96  per  cent  of  clay  substance.  This  point  is  plotted  in  the  first  column. 
The  point  representing  the  percentage  of  fine  silt  is  then  plotted  in  the 
next  column,  and  so  on  with  the  other  sizes.  These  points  are  then 


N.  J.  Geol.  Surv.,  Final  Report,  Vol.  VI,  p.  87,  1904. 


126 


CLAYS 


connected  with  a  curved  line.  In  the  same  way  the  percentages  of  the 
different  sizes  of  grains  of  the  other  samples  were  plotted  and  connected 
by  curved  lines.  The  lines  are  drawn  in  different  ways,  so  that  those 
representing  the  different  clays  can  be  more  readily  distinguished  at  a 
glance.  From  a  study  of  this  table  it  is  seen  that  the  clay  having  the 


FIG.  31. — Curves  showing  relation    of  texture  to  tensile  strength.     (After  Ries? 
N.  J.  Geol.  Surv.,  Fin.  Kept.,  VI,  p.  89,  1904.) 

lowest  tensile  strength  (No.  5)  contains  a  very  high  percentage  of  the 
finest  clay  particles,  furfhermore,  the  clay  having  the  second  lowest 
tensile  strength  (No.  4)  contains  the  largest  percentage  of  sand  (42.9 
per  cent).  From  this  it  appears  that  an  excess  of  either  coarse  or  fine 
grains  lowers  the  tensile  strength.  On  the  other  hand,  in  those  clays 
having  the  highest  tensile  strength  the  percentages  of  fine,  medium,  and 


PHYSICAL  PROPERTIES  OF   CLAY 


127 


coarse  particles  are  more  nearly  equal.  This  is  perhaps  what  might 
be  expected,  for  if  the  tensile  strength  is  due  to  the  interlocking  of  the 
grains,  a  mixture  of  different  sizes  would  fit  together  more  closely  than 
if  particles  of  one  size  predominated,  as  in  Nos.  4  and  5  of  the  table, 
It  is  rather  difficult,  however,  to  compare  these  results  with  Orton's, 
as  in  his  artificial  mixtures  the  non-plastic  particles  were  of  uniform  size, 
while  in  the  natural  mixtures  a  variety  of  sizes  existed. 

Beyer  and  Williams  *  reached  somewhat  similar  conclusions  at  about 
the  same  time,  their  work  on  the  mechanical  analyses  of  the  loess-clays 
indicating  that  the  clays  showing  the  highest  tensile  strength  were  the 
ones  in  which  there  was  the  most  evenly  proportioned  amounts  of  the 
sizes  of  the  grains  represented,  therefore  those  possessing  a  large  propor- 
tion of  excessively  fine  particles  or  those  running  high  in  some  inter- 
mediate size  of  grain  are  weaker.  The  following  mechanical  analyses 
made  by  them  indicate  this : 

MECHANICAL  ANALYSES  OF  IOWA  LOESS  CLAYS 


Size  of  clay  particles. 

ell 

Clay. 

Loss  at 
230°. 

Above 

.lto.05 
mm. 

.05  to 
.01  mm. 

.01  to 
.003 

Below 
.003 

Total 
per 

cent. 

if. 

£•3.3 

incl. 

incl. 

incl. 

mm. 

>•%£ 
<$ 

Besley,  Council  Bluffs, 

top  clay  

1.55 

3.44 

22.10 

49.11 

13.44 

10.35 

99.99 

149 

Gethman,  Gladbrook  . 

2.59 

5:19 

22  .46 

32.04 

14.15 

23.55 

99.98 

279 

Besley,  Council  Bluffs, 

bottom  clay  

2.04 

1.62 

25.26 

29.72 

17.85 

23.  74 

100.23 

244 

If  the  theory  of  interlockment  is  true,  then  it  should  be  possible  to 
make  a  mixture  of  two  clays  whose  tensile  strength  is  higher  than  that 
of  either  of  the  clays  alone  or  vice  versa. 

The  writer2  has  noted  a  case  of  two  clays  from  near  Asbury  Park, 
N.  J.  One  of  these  was  a  slightly  gritty,  black  clay,  with  an  average 
tensile  strength  of  182  Ibs.  per  square  inch.  The  other  was  a  plastic 
loam,  whose  average  tensile  strength  was  137  Ibs.  per  sq.  in.  A  mixture 
of  the  two  in  equal  proportions,  however,  had  an  average  tensile  strength 
of  258  Ibs.  per  sq.  in. 

Another  clay  from  a  different  formation  had  an  average  tensile  strength 
of  108  Ibs.  per  sq.  in.,  while  a  mixture  of  equal  parts  of  this  clay  and  a 


1  la.  Geol.  Surv.,  Vol.  XIV,  p.  102,  1904. 

2  N.  J.  Geol.  Surv.,  Final  Report,  Vol.  VI,  p.  90,  1904. 


128  CLAYS 

somewhat  coarse  sand  had  a  tensile  strength  of  but  65  Ibs.  per  sq.  in., 
the  decrease  being  evidently  due  to  the  excess  of  sand. 

Shrinkage 

All  clays  shrink  in  drying  and  burning,  the  former  loss  being  termed 
the  air-shrinkage  and  the  latter  the  fire-shrinkage. 

Air-shrinkage. — In  a  clay  which  is  perfectly  dry  all  the  grains  are 
in  contact,  but  between  them  there  will  be  a  variable  amount  of  pore- 
space  depending  on  the  texture  of  the  clay.  The  volume  of  this  pore- 
space  is  indicated  somewhat  by  the  quantity  of  water  that  will  be 
absorbed  without  the  clay  changing  its  volume,  this  water  filling  in 
the  space  between  the  grains.  It  may  be  termed  pore  water. 

The  presence  of  more  water  than  is  required  to  fill  the  spaces  between 
the  grains  produces  a  swelling  of  the  mass,  and  in  this  condition  each 
grain  is  regarded  as  being  surrounded  by  a  film  of  water;  but  while  the 
grains  still  mutually  attract  each  other  the  attraction  is  less  than  in 
the  dry  clay,  and  the  mass  yields  readily  to  pressure.  An  excess,  how- 
ever, separates  the  clay  particles  to  such  an  extent  that  the  clay  softens 
and  runs.  A  clay  will  therefore  continue  to  swell  as  water  is  added 
to  it,  until  the  amount  becomes  too  great  to  permit  it  to  retain  its 
shape. 

Some  clays  absorb  very  little  water,  while  others  take  up  a  large 
quantity,  and  G.  P.  Merrill1  mentions  one  from  Wyoming  which  when 
placed  in  a  measuring-flask  absorbed  and  retained  sufficient  water  to 
increase  its  bulk  eightfold. 

When  a  clay  has  been  mixed  with  water  and  set  aside  to  dry  evap- 
oration of  the  moisture  commences  and  the  particles  of  clay  draw  closer 
together,  causing  a  shrinkage  of  the  mass.  This  will  continue  until 
all  the  particles  come  in  contact,  but  since  they  do  not  fit  together 
perfectly  there  will  still  be  some  pore-spaces  left  between  the  grains, 
and  these  will  hold  moisture  which  cannot  be  driven  off  except  by 
heating  at  100°  C.  The  air-shrinkage  may  therefore  cease  before  all 
the  water  has  passed  off. 

The  amount  of  air-shrinkage  is  usually  low  in  sandy  clays,  at  times 
being  under  1  per  cent  in  coarsely  sandy  ones,  while  it  is  high  in  very 
plastic  clays  or  in  some  very  fine-grained  ones,  reaching  at  times  as 
much  as  12  or  15  per  cent.  Five  or  six  per  cent  is  about  the  average 
seen  in  the  manufacture  of  clay  products. 

1  The  Non-metallic  Minerals,  p.  233. 


Or  THF 

"NIVERSITY 

OF 
PHYSICAL  PROPERTIES  OF  CLAY 

All  clays  requiring  a  high  percentage  of  water  in  mixing  do  not 
show  a  high  air-shrinkage.  The  air-shrinkage  of  a  clay  will  not  only 
vary  with  the  amount  of  water  added,  but  also  with  the  texture  of 
the  materials. 

Sand  or  materials  of  a  sandy  nature  counteract  the  shrinkage,  and 
are  frequently  added  for  this  purpose,  but,  since  they  also  render  the 
mixture  more  porous,  they  facilitate  the  drying  as  well,  permitting 
the  water  to  escape  more  readily,  and  reducing  the  danger  from  crack- 
ing. If  the  sand  added  to  dilute  the  shrinkage  is  refractory  it  also 
aids  the  clay  in  retaining  its  shape  during  burning. 

The  effect  of  sand  on  a  clay  is  well  seen  from  the  following  experi- 
ment with  a  clay  from  Herbertsville,  N.  J.1 


Clay.  . 

Per  cent 
water 
required. 

32.6 

Per  cent 
air- 
shrinkage. 
5.3 

Tensile 
strength, 
Ibs.  per  sq.  in. 

108 

Clav  +  50%  sand.  . 

15.6 

3.3 

65 

From  the  above  it  is  seen  that  the  addition  of  50  per  cent  of  sharp 
sand  reduced  the  amount  of  water  required  a  little  over  one  half.  The 
air-shrinkage  was  reduced  37.73  per  cent,  but  it  was  accompanied  by 
a  loss  in  the  tensile  strength  of  nearly  40  per  cent. 

Fire-shrinkage. — All  clays  shrink  during  some  stage  of  the  burning 
operation,  even  though  they  may  expand  slightly  at  certain  tempera- 
tures. The  fire-shrinkage,  like  the  air-shrinkage,  varies  within  wide 
limits,  the  amount  depending  partly  on  the  quantity  of  volatile  ele- 
ments, such  as  combined  water,  organic  matter,  and  carbon  dioxide, 
and  partly  on  the  texture  and  fusibility. 

Fire-shrinkage  begins  at  a  dull-red  heat,  or  about  the  point  at  which 
chemically  combined  water  begins  to  pass  off,  and  reaches  its  maxi- 
mum when  the  clay  vitrifies,  but  does  not  increase  uniformly  up  to 
that  point.  The  clay  worker,  however,  always  tries  to  get  a  low  fire 
shrinkage,  using  a  mixture  of  clays  if  necessary. 

After  the  expulsion  of  the  volatile  elements  the  clay  is  left  in  a  por- 
ous condition,  until  the  fire-shrinkage  recommences. 

In  the  table  2  on  the  next  page  there  are  given  the  results  of  a  series 
of  tests  made  on  eight  different  clays,  which  were  burned  at  tempera- 
tures 100°  C.  apart  from  500°  C.  (932°  F.)  up  to  1100°  C.  (2012°  F.) 
inclusive.2 

1  N.  J.  Geol.  Surv.,  Final  Report,  Vol.  VI,  p.  92,  1904. 

2  Ibid.,  p.  94,  1904. 


130 


CLAYS 


TABLE  SHOWING  PROGRESSIVE  SHRINKAGE  AND  Loss  OF  WEIGHT  AT  DIFFERENT 

TEMPERATURES 


6 

i 

o^o 

600°  C. 

700°  C. 

800°  C. 

900°  C. 

1000°  C. 

1100°C. 

jf 

a 

1112°  F. 

1292°  F. 

1472°  F 

1652°  F. 

1832°  F. 

2012°  F. 

c 

j 

31" 

1 

be 

«* 
to 

i 

1 

60 

_c 
bj 

1 

"o 

.Sf 

1 

1 

1® 

1 

£  • 

£ 

03 

1 

Is 

1 

la 

8 

1 

g 

8 

N 

L 

L 

§3 

^ 

§  c 

8-c 

i| 

!! 

i| 

^ 

§1 

a 

£ 

£ 

r 

r 

£J- 

£~ 

£" 

|5 

£ 

£- 

pT 

£ 

£•" 

£* 

648 

9.0 

2  69 

6.38 

1.72 

0.3 

0.70 

.0 

0.88 

0 

0.56 

0 

0.19 

0.7 

0.38 

4.0 

655 

4.6 

1.36 

6.10 

1.38 

0.0 

0.55 

.0 

0.33 

0 

0.33 

0 

0.12 

0.7 

0.21 

2.4 

663 

5.3 

1.50 

4.24 

1.37 

0.7 

0.35 

.3 

0.05 

0 

0.27 

0 

+  0.06 

0.0 

0.19 

1.3 

665 

7.0 

1.43 

8.65 

1.07 

0.3 

0.48 

.0 

0.39 

0 

0.12 

0 

0.10 

2.7 

0.00 

12.6 

696 

5.6 

3.48 

9.42 

2.61 

0.4 

1.61 

.0 

0.46 

0 

0.33 

0 

0.14 

1.3 

0.22 

4.7 

703 

1.0 

0.63 

2.52 

1.05 

0.0 

0.26 

.0 

0.10 

0 

0.02 

0 

0.09 

1.4 

0.03 

0.0 

717 

8.0 

3.29 

5  .  32 

1.70 

0.3 

0.83 

.0 

0.41 

0 

0.49 

0 

0.34 

1.3 

0.24 

4.0 

728 

2.0 

0.70 

3.23 

1.03 

0.6 

0.61 

.0 

0.22 

0 

0.15 

0 

0.10 

1.3 

0.12 

2.7 

Explanation  of  table. — The  clays  tested  were  the  following: 

648.  Fat,  black,  micaceous  clay,  of  Clay  Marl  I  from  Maple  Shade, 
N.  J. 

655.  A  clay  marl.     Exact  locality  unknown. 

663.  A  Pleistocene  clay  from  Vineland,  N.  J. 

665.  A  yellow,  finely  gritty,  Cohansey  clay,  heavily  stained  with 
limonite  from  Toms  River,  N.  J. 

696.  Black,  Asbury  clay  from  west  of  Asbury  Park,  N.  J. 

703.  Sandy,  Raritan  clay  from  near  Fish  House,  N.  J. 

717.  A  very  plastic  clay  from  Clay  Marl  III,  south  of  Woodbury, 
N.J. 

728.  Hudson  River  shale  from  Port  Murray,  N.  J. 

The  bricklets  had  been  standing  in  a  warm  room  for  several  weeks, 
and,  although  they  appeared  perfectly  dry,  they  were  placed  in  a  hot- 
air  bath  and  kept  at  a  temperature  of  110°  C.  for  a  day,  being  weighed 
both  before  and  after.  This  drove  off  the  moisture  remaining  in  the 
pores,  and  the  resulting  loss  in  weight  indicated  in  the  third  column  of 
the  above  table  shows  the  quantity  of  moisture  that  may  remain  in  a 
brick  after  the  air-shrinkage  has  ceased.  It  is  least  in  the  sandy,  lean 
clays  and  highest  in  the  black  one,  which  is  colored  by  organic  matter. 
The  second  column  indicates  the  per  cent  of  air-shrinkage,  calculated 
upon  the  length  of  a  freshly  molded  bricklet.  The  fourth  column,  headed 
500°  C.  (932°  F.),  gives  the  loss  in  weight  from  the  thoroughly  dried 


PHYSICAL  PROPERTIES  OF  CLAY  131 

condition  up  to  500°  C.,  calculated  on  the  weight  of  the  air-dried  sample. 
The  following  columns  give  the  additional  loss  in  weight  for. each  100°  C. 
(180°  F.),  as  well  as  the  fire-shrinkage  taking  place  in  this  temperature 
interval.  From  an  inspection  of  the  table  it  is  seen  that  most  of  the 
volatile  substances,  such  as  the  chemically  combined  water  contained 
in  the  hydrous  aluminum  silicate,  mica,  or  limonite,  and  organic  matter, 
pass  off  before  500°  C.  (932°  F.),  and  that  an  additional  appreciable 
amount  is  expelled  between  500°  C.  and  600°  C.  Between  600°  C. 
(1112°  F.)  and  1100°  C.  (2012°  F.)  there  was  a  small  but  steady  loss, 
while  in  one  case  (No.  663)  there  was  even  a  gain  in  weight  at  1000°  C. 
(1832°  F.).  Two  samples,  Nos.  696  and  665,  showed  a  high  loss  at 
500°  C.  and  600°  C.,  as  compared  with  the  others,  but  this  was  due  to 
the  former  containing  considerable  organic  matter,  and  the  latter  having 
a  very  high  percentage  of  limonite,  which  would  supply  an  additional 
quantity  of  chemically  combined  water. 

The  amount  of  fire-shrinkage  shown  by  these  samples  is  equally 
interesting,  for  it  is  seen  that,  although  the  loss  in  weight  between  500°  C. 
(932°  F.)  and  900°  C.  (1652°  F.)  is  considerable,  still  there  is  little  or 
even  no  shrinkage,  so  that,  after  the  volatile  elements  have  been  driven 
off,  the  clay  must  be  very  porous,  and  remains  so  until  the  fire-shrinkage 
begins  again.  From  the  table  it  will  be  seen  that,  with  one  exception, 
no  shrinkage  occurred  between  600°  C.  (1112°  F.)  and  900°  C.  (1652°  F.); 
but  between  900°  C.  (1652°  F.)  and  1000°  C.  (1832°  F.),  all  except  No. 
663  decreased  in  size,  and  there  was  an  additional  but  greater  shrinkage 
between  1000°  C.  (1832°  F.)  and  1100°  C.  (2012°  F.).  None  of  the 
brick'ets  became  steel-hard,  that  is,  sufficiently  hard  to  resist  scratch- 
ing with  a  knife,  until  1000°  C.  (1832°  F.),  or  even  1100°  C.  (2012°  F.). 
In  the  case  of  those  burning  red,  a  good  red  coloration  began  to 
appear  at  1000°  C.  (1832°  F.).  From  this  it  can  be  seen,  and  this 
is  a  fact  already  known,  that,  up  to  600°  C.  (1112°  F.),  a  clay  should 
be  heated  slowly;  but  from  that  point  up  to  1000°  C.  the  tempera- 
ture can  be  raised  quite  rapidly,  unless  much  carbonaceous  matter  is 
present.  The  gradual  burning-off  of  this  carbon  is  well  shown  in 
Fig.  19,  which  represents  a  series  of  bricks  taken  from  a  kiln  at 
regular  intervals  as  the  burning  proceeded.  Further  heating  should 
be  done  slowly,  as  the  shrinkage  recommences  at  the  last-mentioned 
temperature. 

Wheeler  l  claims  that  the  most  potent  factor  in  fire-shrinkage  is  the 
size  of  grain :  the  finer  it  is,  the  greater  the  fire-shrinkage. 

1  Mo.  Geol.  Surv.,  Vol.  XI,  p.  121,  1897. 


132  CLAYS 

Since  many  clays,  when  used  alone,  shrink  to  such  an  extent  as  to 
cause  much  loss  from  warping  and  cracking,  it  is  necessary  to  add  mate- 
rials which  of  themselves  have  no  fire-shrinkage,  and  so  decrease  the 
shrinkage  of  the  mixture  in  burning.  Sand  or  sandy  clays  are  the 
materials  most  commonly  used  for  this  purpose,  but  ground  bricks 
(grog),  and  even  coke  or  graphite,  may  be  employed.  These  materials 
serve  not  only  to  decrease  the  shrinkage  in  drying  and  burning,  but  also 
tend  to  prevent  blistering  in  an  easily  fusible  ferruginous  clay  when  hard- 
fired.  They  furthermore  add  to  the  porosity  of  the  ware,  and  thus 
facilitate  the  escape  of  the  moisture  in  drying  and  in  the  early  stages 
of  burning,  as  well  as  enabling  the  product  to  withstand  sudden  changes 
of  temperature.  If  sand  is  added  for  this  purpose,  it  may  act  as  a  flux 
at  high  temperatures,  and  this  action  will  be  the  more  intense  the  finer 
its  grain. 

Large  particles  of  grog  are  undesirable,  especially  if  they  are  angular 
in  form,  because,  in  burning,  the  clay  shrinks  around  them,  and  the  sharp 
edges,  serving  as  a  wedge,  open  cracks  in  the  clay,  which  may  expand 
to  an  injurious  degree.  Large  pebbles  will  do  the  same,  and  at  many 
common  brickyards  it  is  not  uncommon  to  see  bricks  split  open  during 
the  burning,  because  of  some  large  quartz-pebble  left  in  the  clay,  as 
the  result  of  improper  screening  of  the  tempering  sand.  For  common 
brick,  the  type  of  sand  used  does  not  make  much  difference,  as  long 
as  it  is  clean;  but  if  sand  is  to  be  added  to  fire-brick  mixtures,  it  should 
be  coarse,  clean,  quartz-sand.  Burned  clay-grog  is  more  desirable  than 
sand  for  high-grade  wares,  since  it  does  not  affect  the  fusibility  of  the 
clay,  or  swell  with  an  increase  of  temperature  as  sand  does,  but  precau- 
tion should  be  taken  to  burn  the  clay  to  its  limit  of  shrinkage  before 
using  it. 

Measurement  of  shrinkage. — A  knowledge  of  the  air-  and  fire-shrink- 
age of  a  clay  is  of  vital  importance  to  the  manufacturer  of  clay-products, 
since,  in  order  to  produce  a  burned  ware  of  the  required  dimensions, 
he  must  know  the  air-  and  fire-shrinkage  of  his  raw  clays. 

The  shrinkage  of  a  clay  may  be  expressed  linearly  or  cubically. 
The  former  is  given  in  percentage  terms  of  the  original  length  of 
the  ware,  and  is  easily  determined  by  direct  measurement.  To  deter- 
mine the  cubical  shrinkage  in  drying,  it  is  necessary  to  carefully 
determine  the  volume  of  clay  when  moist  and  again  when  dry,  while 
the  difference  in  volume  between  the  latter  and  that  of  the  burned  clay 
gives  the  cubic  fire-shrinkage. 

Determination  of  volume. — The  change  in  volume,  to  be  determined 
for  getting  the  cubic  shrinkage,  is  measured  by  means  of  a  Seger  volu- 


PHYSICAL  PROPERTIES  OF  CLAY 


133 


meter  (Fig.  32).  This  consists  of  a  four-litre,  wide-mouthed,  glass-stop- 
pered jar.  A  circular  opening  in  the  center 
of  the  stopper  is  fitted  with  the  ground- 
end  of  a  short  glass  tube  m,  which  ex- 
pands above  into  a  bulb  b,  and  is  again 
contracted  above  it.  The  jar  has  a 
glass  stopcock  e  near  its  base,  which  is 
connected  above  with  a  burette  a  of 
125  c.c.  capacity,  and  graduated  to 
tenths.  The  upper  end  of  the  burette 
also  widens  to  a  bulb  /,  from  the  top 
of  which  there  extends  a  bent  tube  for 
the  attachment  of  a  rubber,  this  tube 
being  used  to  draw  the  liquid  into  the 
burette. 

When  the  stopcock  in  the  lower  part 
of  the  burette  is  open,  and  the  liquid 
filled  in  jar  up  to  the  mark  on  the  small 
glass  tube  m,  the  liquid  stands  at  the 
zero-point  in  the  burette. 

The  method  of  using  the  apparatus, 
together  with  the  results  obtained  on  a 
number  of  Iowa  clays,  was  as  follows:1 

"  To  use  the  volumeter  for  determining 
the  volume  of  clay,  it  is  filled  with  oil, 
ordinary  kerosene  with  a  specific  gravity 
of  0.8  (which  must  be  accurately  known)  FlG-  32.— Seger's  volumeter,  for 

having  been  found  to  give    satisfactory     determininS  P0™8^  and   spe. 

J       cific  gravity, 
results. 

"  After  filling  the  jar  the  burette  is  drawn  full  of  the  liquid  by  suc- 
tion through  the  rubber  tube,  and  held  full  by  turning  the  burette- 
valve  or  by  means  of  a  pinch-cock  on  the  rubber.  The  stopper  is  now 
removed  and  the  test-piece  of  the  clay,  which  is  still  plastic  and  per- 
meated with  water,  is  carefully  wiped  dry  of  the  coating  film  and  put 
in.  The  test-pieces,  which  were  approximately  3  inches  long,  were 
allowed  to  dry  till,  on  picking  up  a  piece  endwise  between  the  thumb 
and  finger,  the  middle  portion  did  not  sag.  This  point  was  noted  care- 
fully and  all  samples  were  treated  in  this  regard  exactly  the  same.  Care 
is  taken  not  to  spatter  any  of  the  liquid  in  placing  the  block  of  clay 


la.  Geol.  Survey,  Vol.  XIV,  p.  107.  1904. 


134  CLAYS 

in  the  jar.  In  order  to  prevent  this,  and  to  avoid  breaking  or  other- 
wise marring  the  test-piece  by  dropping  it  into  the  vessel,  a  small  wooden 
float  or  support  by  which  the  clay  may  be  carefully  let  down  into  the 
liquid  is  advantageous.  This  float  is  conveniently  made  with  a  small 
eye  or  hook  near  each  end  so  that  it  may  be  handled  by  reaching  in  with 
two  stiff  bent-wire  rods.  Some  such  arrangement  as  this  is  found  quite 
necessary  in  handling  raw  clays,  but  can  be  dispensed  with  when  the 
clays  are  burned.  The  stopper  is  now  replaced,  and  by  releasing  the 
pinch-cock  d  oil  from  the  burette  is  allowed  to  flow  back  into  the  jar 
until  it  stands  at  the  mark  on  the  short  tube. 

"  The  volume  of  the  clay  is  then  indicated  by  the  height  of  the  liquid 
in  the  burette  above  the  zero  mark.  The  piece  of  clay  is  taken  out 
and  placed  to  dry  while  the  volumeter  is  again  filled  to  the  zero  points 
to  be  ready  for  the  next  test. 

"  When  dry  the  clay  is  heated  to  230°  F.  to  expel  all  hygroscopic 
moisture  and  after  weighing  it  is  placed  in  a  vessel  of  oil  until  saturated. 
This  is  found  to  require  from  three  to  six  hours  for  small  test-pieces 
of  approximately  3X1JX1J  inches.  When  saturated  the  piece  is 
again  weighed  and  its  volume  measured  as  before.  Having  now  the 
wet  and  dry  volumes,  the  percentages  of  cubical  shrinkage  in  drying 
are  easily  calculated. 

"  In  measuring  fire-shrinkage  the  same  test-pieces  were  employed 
that  were  made  use  of  in  determining  drying  shrinkage.  They  were 
placed  in  a  small  muffle-furnace  and  burned  to  a  temperature  of  700° 
to  800°  C.  By  burning  at  this  heat  dehydration  and  oxidation  of  the 
clay  were  completed.  It  is  about  the  temperature  at  which  common, 
porous  red-building  brick  is  burned.  For  the  large  number  of  clays 
vitrification  has  not  yet  begun  at  this  heat,  and  they  are  left  in  the  most 
porous  condition  attained  during  any  part  of  the  burning  process. " 

The  results  of  a  number  of  determinations  made  on  Iowa  clays r 
giving  the  cubic  air-  and  fire-shrinkage,  as  well  as  the  porosity  of  the 
dried  and  burned  clay,  are  tabulated  on  page  135. 

It  will  be  seen  from  the  above  table  that  in  two  cases  there  was 
a  slight  expansion  of  the  mass,  as  indicated  by  the  minus  fire-shrinkage. 

Porosity 

The  porosity  of  a  clay  may  be  defined  as  the  volume  of  the  pore- 
space  between  the  clay  particles,  expressed  in  percentages  of  the  total 
volume  of  the  clay,  and  depends  on  the  shape  and  size  of  the  particles 
making  up  the  mass.  The  maximum  porosity  would  be  found  in  a 


PHYSICAL  PROPERTIES  OF  CLAY 


135 


POROSITY  AND  CUBIC  SHRINKAGE  OF  IOWA  CLAYS 


Clay. 

Porosity  of 
un  burned 
clay. 

Porosity  of 
burned 
clay. 

Cubic 
air- 
shrinkage. 

Cubic 
fire- 
shrinkage. 

Flint  Brick  Co    bottom,  of  bank 

30  04 

26  94 

9.44 

1    99 

Flint  Brick  Co    middle  of  bank 

23  00 

24  74 

23  34 

1  82 

Flint  Brick  Co.,  top  of  bank  

17.31 

22.31 

26.23 

4  24 

Corey  Pressed  Brick  Co.,  red-burning  

30.10 

33.24 

16.94 

2  37 

Corey  Pressed  Brick  Co    buff-burning 

28  10 

29  59 

27  00 

2  91 

Colesburg  Potters'  Clay      

28.36 

25.51 

18  25 

5  92 

Granite  Brick  Co    top  stratum  

23.00 

25.57 

4  86 

-2  88 

American  Brick  &  Tile  Co.,  plastic  shale  

26.71 
29.77 

30.46 
32.66 

21.52 
6  83 

0.00 
-2  47 

clay  made  up  entirely  of  spherical  grains  of  the  same  size,  but  such 
clays  are  practically  unknown.  On  the  contrary,  all  clays,  so  far  as 
known,  are  made  up  of  a  mixture  of  sizes,  which  greatly  reduces  the 
porosity.  In  general  we  may  say,  however,  that  increasing  fineness 
means  increasing  pore-space. 

The  rapidity  with  which  a  clay  absorbs  water  is  not  to  be  regarded 
as  a  criterion  of  its  porosity,  for  two  clays  of  the  same  porosity  may 
differ  in  grain,  on  which  account  the  coarse-grained  one  will  absorb 
water  more  rapidly  than  the  fine-grained  one. 

The  porosity  of  a  clay  is  of  importance,  because  it  influences  the 
behavior  of  it  towards  water,  heat,  etc.  These  effects  may  be  sum- 
marized as  follows: 

Porosity  influences  the  amount  of  water  which  a  clay  will  absorb, 
or  the  amount  required  to  make  them  plastic,  and  this  will  in  turn 
influence  the  air-shrinkage. 

The  possible  rate  of  safe  drying  depends  on  the  amount  of  water 
absorbed  and  the  facility  with  which  it  can  escape;  large  pores  per- 
mitting the  water  to  escape  rapidly.  Small  pores,  on  the  other  hand, 
retard  both  the  absorption  and  evaporation  of  the  water. 

In  the  burned  clay,  too,  the  porosity  has  to  be  considered,  for  all 
clays  after  burning  are  more  or  less  porous  unless  burned  to  vitrification. 
In  most  clay  products  a  low  porosity  is  desirable  in  order  to  increase 
its  resistance  to  the  weather.  If  a  product  is  very  porous,  it  will  absorb 
considerable  water,  which  on  freezing  expands.  If  the  pores  are  large, 
the  pressure  exerted  by  the  expanding  water  on  freezing  will  be  relieved 
by  the  exudation  of  small  ice  crystals  from  the  pores,  and  no  harm 
results.  If,  on  the  other  hand,  the  pores  are  small,  this  cannot  occur, 
and  a  sufficient  pressure  may  be  exerted  from  the  contained  ice  to  dis- 
integrate the  mass.  With  close-textured  clays  the  porosity  may  be 
so  small  that  not  enough  water  can  enter  to  cause  any  harm. 


136  CLAYS 

The  porosity  of  the  clay  in  either  its  raw  or  burned  condition  is 
determined  by  means  of  a  Seger  volumeter  described  under  Shrinkage. 
The  porosity  percentage  is  determined  by  the  formula 

7 


in  which  F  =  volume  of  dry  test-piece; 

</  =  difference  in  weight  between  dry  and  saturated  test-piece 

or  the  weight  in  grams  of  oil  absorbed  ; 
s  =  specific  gravity  of  oil. 

In  testing  the  porosity  of  burned  wares  distilled  water  can  be  used. 
The  specific  gravity  of  this  at  ordinary  temperatures  can  be  taken  as 
unity,  and  s  therefore  disappears  from  the  formula,  g  becomes  cubic 
centimeters,  and  the  expression  reduces  to 

P  =  |rX100. 


Specific  Gravity 

The  specific  gravity  of  a  clay  is  not  a  factor  of  great  economic  import- 
ance, although  it  has  to  be  known  in  order  to  determine  the  porosity 
by  the  formula  mentioned  under  that  head.  Since  also  it  is  related  to 
the  density  of  the  mass,  which  no  doubt  exerts  some  influence  on  the 
fusibility  of  the  material,  it  is  required  for  the  determination  of  the 
fusibility  factor  by  certain  methods  (see  under  Fusibility). 

This  is  assuming  that  the  more  compact  a  clay  the  lower  its  fusion 
point,  and  it  has  been  pointed  out l  that  according  to  this  a  clay  might 
have  one  specific  gravity  as  it  came  from  the  bank,  and  this  \vould 
change  with  each  manipulation.  A  knowledge  of  the  specific  gravity 
of  clay  based  on  this  conception  is  of  little  value,  however,  since  it  is 
not  the  true  specific  gravity  which  depends  on  the  mineralogical  composi- 
tion and  not  the  porosity.  As  such,  the  specific  gravity  of  the  clay  will 
remain  constant,  whatever  its  condition. 

There  is  comparatively  little  variation  in  the  specific  gravity  of  the 
minerals  most  abundant  in  clay,  as  can  be  seen  from  the  following: 

Kaolinite 2.6  Quartz 2.65 

Calcite 2.71         Feldspars.  . . .   2 . 55-2 . 75 

Biotite 2.7-3.1  Muscovite.  .  .  2 . 76-3 

1  la.  Geol.  Surv.  XIV.  p.  114,  1904. 


PHYSICAL   PROPERTIES   OF  CLAY  137 

Iron  oxides  would  be  heavier;  still  they  form  but  a  small  percentage 
of  the  entire  mass. 

Some  of  the  recorded  specific  gravities  of  clay  fall  considerably 
below  the  average  specific  gravity  of  that  of  the  common  minerals  found 
in  clay,  which  may  be  due  to  the  method  of  determination  used. 

In  a  series  of  New  Jersey  clays  tested  by  the  writer  the  gravity 
ranged  from  2.34  to  2.84.1 

Beyer  and  Williams  give  the  range  of  Iowa  clays  tested  as  from  2.32 
to  2.64.2 

The  Missouri  clays  tested  by  Wheeler3  ranged  from  1.66  to  2.64, 
while  the  determinations  of  Smock 4  on  the  New  Jersey  clays  ranged 
from  1.80  to  2.60. 

The  lower  values  obtained  by  Wheeler  and  Smock  are  no  doubt  due 
to  the  method  used  by  them,  which  consisted  in  coating  a  lump  of  clay 
in  paraffin  so  that  it  could  not  slack  in  water,  and  then  determining  the 
weight  in  water  of  this  lump. 

Determination  of  specific  gravity. — The  simplest  method  of  determin- 
ing the  true  specific  gravity  of  a  clay  is  by  means  of  a  pycnometer  of  the 
ordinary  type,  or  it  can  also  be  made  with  a  Seger  volumeter,  using  the 
formula 

/nr 

Sp'  gr'  =V(100  per  cent)- P' 
in  which 

G  =  actual  weight  or  mass  of  test-piece  when  dry; 
V—  apparent  volume,  or  clay  plus  pore-space; 
P  =  percentage  of  porosity. 

Fusibility 

All  clays  fuse  at  one  temperature  or  another,  the  temperature  of 
fusion  depending  on  (1)  the  amount  of  fluxes;  (2)  the  size  of  grain  of  the 
refractory  and  non-refractory  particles;  (3)  the  homogeneity  of  the  mass; 
(4)  the  condition  of  the  fire,  whether  oxidizing  or  reducing;  and  (5)  the 
form  of  chemical  combination  of  the  elements  contained  in  the  clay. 

The  changes  occurring  in  the  early  stages  of  burning  have  been 
referred  to  under  Fire-shrinkage  and  Chemical  Properties,  and  in  the 
table  given  on  page  130  it  was  seen  that  the  clay  had  become  steel-hard, 
due  to  a  partial  fusion  of  some  of  the  particles. 

1  N.  J.  Geol.  Surv.,  Final  Report,  Vol.  VI,  p.  114,  1904. 

2  la.  Geol.  Surv.,  Vol.  XIV,  p.  116,  1904. 

3  Mo.  Geol.  Surv.,  Vol.  XI,  p.  562  et  seq.,  1896. 
1  N.  J.  Geol.  Surv.,  Report  on  Clays,  1878. 


138  CLAYS 

In  considering  the  changes  which  occur  in  the  fusion  of  clays  it  is 
necessary  to  remember  that  clay  is  not  a  substance  of  definite  chemical 
composition,  but  consists  of  a  mixture  of  minerals  each  having  its  own 
melting-point. 

When  clays  undergo  a  fusion  process  they  do  not  soften  at  once,  but 
melt  with  comparative  slowness.  This  is  not  surprising  when  we  con- 
sider their  heterogeneous  composition,  and  may  account  for  their  slow 
softening  as  one  kind  of  a  mineral  after  another  fuses.  As  soon  as  a 
softening  of  one  or  more  of  the  mineral  grains  occurs  interreactions 
between  the  different  ones  begin,  the  number  involved  increasing  until 
all  constituents  of  the  mass  are  involved.  In  most  cases  no  reaction 
occurs  between  any  of  the  grains  until  one  melts,  but  it  is  not  necessary 
to  reach  the  fusion-point  of  each  before  it  can  react  with  the  others. 

Thus  carbonate  of  lime  and  carbonate  of  magnesia  lose  their  carbon 
dioxide  at  a  comparatively  low  temperature,  and  the  remaining  oxides 
of  these  elements  are  highly  refractory  if  heated  alone.  If,  however. 
they  are  mixed  with  other  minerals,  they  appear  to  react  with  them  long 
before  their  fusion-points  are  reached. 

On  account  of  the  gradual  softening  of  clays  when  heated  to  their 
fusion-point  Wheeler  has  suggested  the  recognition  of  the  following 
stages  : 

Incipient  vitrification. — In  this  stage  the  clay  has  softened  sufficiently 
to  make  the  grains  stick  together,  and  enough  to  prevent  the  recognition 
of  any,  except  the  larger  ones.  The  particles  have  not,  however,  soft- 
ened sufficiently  to  close  up  all  pores  of  the  mass. 

Complete  vitrification. — A  further  heating  of  the  clay,  through  a 
variable  temperature  interval  ranging  from  about  27.7°  C.  (50°  F.)  to 
111.1°C.  (200°  F.),  or  sometimes  even  more,  produces  an  additional 
softening  of  the  grains  sufficient  to  close  up  all  the  pores  and  render  the 
mass  impervious.  Clays  burned  to  this  condition  of  complete  vitrifica- 
tion show  a  smooth  fracture  with  a  slight  luster.  The  attainment  of 
this  condition  also  represents  the  point  of  maximum  shrinkage. 

Viscosity. — A  still  further  but  variable  rise  in  the  temperature  is 
accompanied  by  both  swelling  and  softening  of  the  clay,  until  it  flows  or 
gets  viscous. 

It  is  sometimes  difficult  to  recognize  precisely  the  exact  attainment 
of  these  three  conditions,  for  the  clay  may  soften  so  slowly  that  the 
change  from  one  to  the  other  is  gradual. 

According  to  Wheeler  1  the  hardness  of  a  clay  when  it  has  reached 
the  first  of  these  three  stages  is  from  6  to  6.5  according  to  Mohs'  scale; 
1  Mo.  Geol.  Survey,  Vol.  XI,  p.  130,  18%. 


PHYSICAL  PROPERTIES  OF  CLAY  139 

or  in  other  words  it  cannot  be  scratched  with  a  knife.  The  temperature 
of  steel-hardness  varies  with  the  character  of  the  material,  impure, 
easily  fusible  clays  becoming  so  at  a  low  temperature,  such  as  cone  05, 
while  others,  such  as  kaolins  and  some  fire-clays,  fail  to  reach  this 
condition  before  cone  5  to  81;  but  with  other  things  equal,  a  highly 
plastic  clay  will  burn  steel-hard  at  a  much  lower  temperature  than  one 
of  low  plasticity. 

The  difference  in  temperature  between  the  points  of  incipient  fusion 
and  viscosity  varies  with  the  composition  of  the  clay.  In  many  calcare- 
ous clays  these  points  are  within  27.7°  C.  (50°  F.)  of  each  other,  while  in 
refractory  clays  they  may  be  277°  C.  (500°  F.)  apart.  The  glass-pot 
clays  which  are  refractory,  but  still  burn  dense  at  a  comparatively  low 
temperature,  approach  the  last-mentioned  condition  quite  closely. 

Wheeler  gives  the  following  figures  of  variation  based  on  the  tests 
of  135  clays.2 


Ran*e'  Character. 

2  75°  F.  Very  calcareous. 

33  300°  F.  Very  impure  clays  and  shales. 

1  1  350°  F.  Less  impure  clays  and  shales. 

63  400°  F.  Fire-clays,  potters'  clays,  kaolins. 

26  500°  F.  Some  china-clays,  pure  fire-clays. 

It  is  of  considerable  practical  importance  to  have  the  points  of  incipient 
vitrification  and  viscosity  well  separated,  because  in  the  manufacture 
of  many  kinds  of  clay-products  the  ware  must  be  vitrified  or  rendered 
impervious.  If,  therefore,  the  temperature  interval  between  the  points 
of  incipient  vitrification  and  viscosity  is  great,  it  will  be  safer  to  bring 
the  ware  up  to  a  condition  of  complete  vitrification  without  the  risk 
of  reaching  the  temperature  of  viscosity  and  melting  all  the  wares'  in  the 
kiln,  because  it  is  impossible  to  control  the  kiln  temperature  within 
a  range  of  a  few  degrees.  In  many  clays  the  point  of  complete  vitrification 
seems  to  be  midway  between  that  of  incipient  vitrification  and  viscosity, 
but  in  others  it  is  not. 

Effect  of  chemical  composition  on  fusibility.  —  Other  things  being 
equal,  the  temperature  of  fusion  of  a  clay  will  fall  with  an  increase  in 
the  percentage  of  total  fluxes.  If  we  compare  the  analyses  of  a  brick- 
clay  and  a  fire-clay,  we  shall  find  that  the  analysis  of  the  former  shows 
perhaps  12  or  15  per  cent  of  fluxing  or  fusible  ingredients,  while  that 
of  the  latter  may  show  only  2  or  3  per  cent,  and  that  their  fusion-points 

1  For  explanation  of  these  see  p.  149. 

2  Mo.  Geol.  Survey,  Vol.  XI,  p.  131,  1896. 


140  CLAYS 

are  perhaps  1093°  C.  (2000°  F.)  and  1644°  C.  (3000°  F.)  respectively. 
But  while  in  general  the  fusion-point  falls  as  the  percentage  of  fluxes 
rises,  it  is  found  that  the  different  fluxes  exert  a  different  fluxing  influence; 
that  is  to  say,  it  requires  more  of  one  than  another  to  bring  about  the 
same  degree  of  fusibility.  Moreover  there  is  a  variation  in  the  tempera- 
ture at  which  the  different  ones  become  active. 

One  of  the  first  investigators  to  throw  some  light  on  this  subject 
was  a  German  by  the  name  of  Richter,  whose  researches  have  become 
classic.  He  formulated  three  laws,  as  follows: 

1.  The  refractory  quality  of  a  clay  of  any  given  proportion  of  silica 
and  alumina  is  most  influenced  by  the  fluxes  in  the  following  order: 
MgO,  CaO,  FeO,  Na20;  K20. 

2.  Chemically   equivalent   quantities   of   these   oxides   exert   equal 
influences  on  the  refractoriness  of  a  given  clay;    that  is,  40  parts  of 
magnesia,  56  parts  of  lime,  72  parts  of  ferrous  oxide,  62  of  soda,  and 
92  parts  of  potash  will  each  produce  an  equal  degree  of  fusion  in  the 
same  quantity  of  the  same  clay. 

3.  If  a  number  of  fluxes  are  present  in  a  clay,  the  fusibility  produced 
will  be  proportional  to  the  sum  of  their  chemical  equivalents.     For 
example,  a  clay  with  the  formula 

0.15  K20  \ 

0.15  CaO  \  '  Al2°3'  2Sl°2 

should  fuse  at  the  same  temperature  as  one  of  the  composition 

0.1  K20  1 

0.1  CaO  | ,  A12O3,  2SiO2. 

0.1  FeO  J 

In  working  out  these  laws,  Richter  used  a  series  of  alumina-silica 
mixtures,  to  which  known  proportions  of  the  fluxes  were  then  added. 

In  his  first  series  he  employed  silica  and  alumina  mixed  in  the  same 
proportions  as  in  kaolinite,  while  in  a  second  but  similar  series  he 
used  a  higher  silica  percentage  than  is  present  in  kaolinite. 

Considering  the  case  of  silica  and  alumina  in  the  proportions  that 
they  exist  in  kaolinite,  it  is  found  that  they  have  a  fusion-point  of  about 
1830°  C.  (3326°  F.),  or  cone  36  of  the  Seger  scale.  The  continued 
addition  of  silica  to  this  lowers  its  fusion-point  until  the  ratio  of  A12O3, 
!7Si02  (or  1:9  by  weight),  is  reached,  the  fusion-point  of  this  being 
about  1650°  C.  (3002°  F.),  or  cone  26,  but  a  continued  increase  of  silica 
raised  it. 


PHYSICAL   PROPERTIES  OF  CLAY 


141 


Silica,  therefore,  is  to  be  regarded  as  a  flux  to  alumina,  at  high  tem- 
peratures, and  should  not,  therefore,  be  present  in  excess  in  refractory 
clays. 


100  $  SiUoa 

FIG.  33. — Diagram  showing  effect  of  silica  on  the  fusion-point  when  mixed  with 
alumina  and  with  kaolin.     (From  Seger's  experiments.) 

Moreover,  the  presence  of  silica  in  a  clay  seems  to  intensify  the  effect 
of  other  fluxes. 

Cramer  l  at  a  later  date  attempted  to  verify  Richter's  experiments, 
but  found  that  the  fluxing  power  of  oxides  is  only  true  in  so  far  as  it 
concerns  kaolinite,  while  in  the  presence  of  free  silica  he  found  the  flux- 
ing power  as  follows:  FeO,  MgO,  CaO,  Na2O,  K20.  In  other  words, 
if  free  silica  is  present  the  oxides  do  not  act  according  to  their  chemical 
equivalency,  72  parts  of  ferrous  oxide,  for  example,  being  more  effec- 
tive than  40  parts  of  magnesia,  etc. 

Important  as  the  results  of  Richter  and  Cramer  are,  the  laws  do 
not  hold  true  for  the  changes  ordinarily  taking  place  in  a  kiln,  even 
though  they  be  burned  to  vitrification.  That  is  to  say,  the  law  only 
holds  true  when  all  the  elements  of  the  clay  can  take  part  in  the  fusion  of 
the  mass;  in  other  words,  when  it  has  reached  a  state  of  complete  fusion. 

In  the  melting  of  a  clay,  a  reaction  occurs  between  the  silica,  alu- 
mina, and  the  various  fluxes,  giving  rise  to  the  formation  probably  of 
complex  silicates,  and  it  is  supposed  that  the  various  elements  enter 
into  combination  in  the  same  form.  Thus  iron,  whatever  its  state  of 

1  Thonindustrie-Zeitung,  1895,  Nos.  40  and  41. 


142  CLAYS 

oxidation  in  the  clay,  is  believed  to  enter  into  combination  in  the  fer- 
rous form,  and  therefore  its  fluxing  power  is  regarded  as  due  to  the 
action  of  ferrous  oxide.  So,  too,  lime  enters  into  combination  as  CaO, 
magnesium  as  MgO,  and  sodium  and  potassium  as  Na2O  and  K2O, 
respectively. 

Richter's  work  on  the  fusibility  of  clays  has  been  more  recently 
discussed  by  Ludwig  1  from  the  view-point  of  modern  chemical  theories: 

"The  fusion  of  silicates  results  in  the  production  of  igneous  solu- 
tions holding  dissolved  various  silicates.  Thus  Seger  Cone  No.  1,  con- 
sisting of  a  mixture  of  feldspar,  kaolin,  quartz,  and  ferric  oxide,  is, 
when  fused,  a  mutual  solution  of  feldspar,  quartz,  augite  or  horn- 
blende. If  we  could  cool  this  mass  slowly,  these  silicates  would  crys- 
tallize out  one  after  the  other.  This  has  actually  been  done  by  Prof. 
Vogt  of  Christiania,  who  has  shown  that  the  temperature  of  fusion 
is  always  highest  when  only  one  definite  silicate  crystallizes  out,  and 
lowest  when  it  represents  a  mixture  of  several  silicates.  This  coin- 
cides perfectly  with  the  general  phenomenon  observed  in  all  solutions, 
namely,  that,  on  dissolving  any  substance,  a  decrease  of  the  melting- 
point  takes  place.  It  is  immaterial  whether  the  melting-point  lies  at 
0°  or  at  1200°  C.  The  compositions  of  the  slags  and  glazes  are  prac- 
tical illustrations,  inasmuch  as  the  most  fusible  combinations  of  either 
kind  of  silicate  are  always  the  most  complex  ones.  When  two  silicates 
are  combined,  they  invariably  result  in  a  mixture  having  a  lower  melt- 
ing-point than  either,  owing  to  the  formation  of  the  so-called  eutectic 
mixture.  Thus,  mono-calcium  silicate  fuses  at  cone  15;  on  adding 
one  molecule  of  silica  to  two  molecules  of  this  silicate,  the  melting-point 
falls  to  cone  7,  but  on  adding  more  quartz  the  fusion-point  again  rises, 
Again,  in  a  clay  containing  besides  silica  and  alumina  the  various  fluxes, 
the  melting-point  is  governed  by  the  fusing-point  of  the  eutectic  mix- 
ture of  these  constituents,  which  represents  the  most  fusible  combina- 
tion possible.  This  explains  also  why  feldspar  begins  its  fusing  effect 
in  a  body  much  below  its  melting-point.  The  eutectic  mixture  is 
invariably  high  in  fluxes  at  the  lower  temperatures,  but  takes  up  more 
and  more  silica  as  the  temperature  is  raised.  Silicates  proper  are  more 
fusible  than  high  alumina  mixtures,  and  hence  more  silica  is  brought 
into  solution  than  alumina,  which  is  dissolved  only  at  high  tempera- 
tures. This  explains  the  fact  that  aluminous  clays  show  the  greatest 
refractoriness.  As  the  solution  increases  in  amount  the  clay  softens, 
and  finally,  when  there  remains  but  little  undissolved  matter,  fusion 

1  Thonindustrie-Zeitung,  XXV111,  p.  773,  1904.  The  abstract  of  the  paper  here 
given  is  that  of  Bleininger,  Trans.  Amer.  Cer.  Soc.,  VII,  p.  275,  1905. 


PHYSICAL  PROPERTIES  OF  CLAY  143 

takes  place.  This  manner  of  melting  is  characteristic  of  solutions 
while  substances  homogeneously  crystalline  melt  suddenly  without  soft- 
ening. Thus  the  final  melting-point  depends  upon  the  ratio  of  the 
alumina  to  the  silica  and  the  amount  and  kind  of  flux. 

11  The  foundation  of  these  fusion  phenomena  is  the  following  general 
law  applying  to  dilute  solutions: 

"  Equi-molecular  quantities  of  different  substances  dissolved  in  equal 
amounts  of  the  same  solvent  lower  the  melting-point  in  the  same  degree. 

"  The  law  applies  to  substances  in  general,  indifferent  as  to  whether 
they  are  bases  or  acids,  the  only  requirement  being  that  they  are  soluble. 
With  reference  to  clay  we  must  therefore  consider  lime,  magnesia,  potash, 
soda,  and  titanic  acid  as  the  dissolved  substances. 

"  If  now  we  are  to  compare  refractory  clays  as  to  their  melting-points 
we  must  calculate  the  molecular  formula  of  each  clay,  making  the  alumina 
equivalent  equal  to  unity  and  adding  the  equivalents  of  various  fluxes, 
•obtaining  thus  a  formula  like 

A12O3  +2. 125S:O2  +0.0755RO. 

"  Since  in  this  expression  there  are  but  two  variables,  Ludwig  plotted 
the  silica  equivalent  as  the  abscissa  of  a  curve  and  ten  times  the  equivalent 
of  the  RO  as  the  ordinate,  and  in  this  manner  he  located  various  Ger- 
man fire-clays  in  a  chart,  verifying  the  clays  by  their  melting-points  in 
Seger  cones. 

"  Richter's  law,  strictly  speaking,  applies  only  to  dilute  solutions,  and 
hence  if  the  amount  of  fluxes  is  considerable  the  law  loses  much  of  its 
force.  If  does  not  apply,  therefore,  completely  to  glazes  or  glasses. 
Differences  from  this  general  law  are  not  due  to  chemical  reasons,  since 
it  does  not  matter  in  what  chemical  combination  a  flux  enters  into  a 
clay,  whether  as  feldspar  or  as  potash,  but  must  be  sought  for  in  the 
different  mechanical  conditions. 

"  Ludwig  summarizes  his  work  in  the  following  conclusions: 

"  1st.  Richter's  law  is  a  special  case  of  the  general  law  of  dilute  solu- 
tions. 

"2d.  This  law  is  restricted  by  the  following  conditions: 

"  (a)  It  applies -only  to  very  dilute  solutions,  that  is  clays  with  a 
small  amount  of  fluxes  and  not  to  brick-clays  or  glazes. 

"  (6)  It  assumes  intimate  mixture. 

"  (c)  Iron  shows  a  different  effect,  due  to  its  two  stages  of  oxidation, 
since  one  molecule  of  ferric  oxide  corresponds  to  two  molecules  of  ferrous 
oxide.  A  given  percentage  of  iron  contains  fewer  molecules  of  ferric 
oxide  than  of  ferrous  oxide,  since  the  former  has  a  higher  molecular 


144  CLAYS 

weight.     On  changing  to  the  ferrous  oxide  the  number  of  molecules  is 
doubled,  and  hence  the  fluxing  effect  is  doubled. 

"  3d.  The  analysis  of  a  fire-clay  is  of  great  importance  in  estimating 
the  refractoriness. 

"  4th.  The  estimation  of  the  refractoriness  by  means  of  the  percent- 
ages of  alumina  and  fluxes  leads  to  erroneous  results." 

Homogeneity. — Unless  the  particles  of  each  element  or  compound 
are  uniformly  distributed  through  the  mass  they  will  not  produce  their 
maximum  effect.  Few  clays  as  they  occur  in  nature  are  perfectly  uniform 
in  composition. 

It  is  sometimes  argued  from  this  that  in  testing  clays  for  their  fusi- 
bility it  is  necessary  to  render  them  as  homogeneous  as  possible,  but  in 
order  to  obtain  results  of  practical  value  the  clay  should  not  be  mixed 
and  ground  up  any  more  than  it  would  be  for  the  particular  class  of 
clay  products  to  which  it  is  adapted. 

Influence  of  texture. — The  size  of  the  mineral  grains  exerts  an 
important  effect  on  the  fusibility  of  the  clay.  Other  things  being  equal, 
a  fine-grained  clay  will  fuse  at  a  lower  temperature  than  a  coarse-grained 
one,  partly  because  finely  divided  particles  can  come  into  more  intimate 
contact,  and  the  air-spaces  being  diminished  the  heat  will  be  transmitted 
better.  Then,  too,  when  the  particles  begin  to  fuse  or  flux  with  each 
other,  this  action  begins  on  the  surface  of  the  grains  and  works  inward 
towards  the  center.  If,  therefore,  the  easily  fusible  grains  are  of  small 
size  they  fuse  more  rapidly,  and  are  more  effective  in  their  fluxing  action 
than  if  the  grains  were  large.  Since  some  of  the  mineral  grains  in  the 
clay  are  more  refractory  than  others,  the  clay  in  the  earlier  stages  of 
fusion  can  be  regarded  as  a  mixture  of  fused  particles  with  a  skeleton 
of  unfused  ones.  If  the  proportion  of  the  former  to  the  latter  is  very 
small  there  will  be  a  strong  hardening  of  the  clay  with  little  shrinkage, 
and  the  burned  clay  will  still  be  porous.  With  an  increase  of  temperature 
and  the  fusion  of  more  particles,  the  pores  fill  up  more  and  more,  and 
the  shrinkage  goes  on  until,  at  the  point  of  vitrification,  the  spaces  are 
completely  filled.  Above  this  point  there  is  no  longer  a  sufficiently 
strong  skeleton  to  hold  the  mass  together,  and  the  clay  begins  to  flow. 
The  conditions  which  influence  the  difference  in  temperature  between 
vitrification  and  viscosity  still  remain  to  be  satisfactorily  explained 
but  it  probably  depends  on  the  relative  amounts  of  fluxes  and  non- 
fluxes  and  the  size  of  grain  of  the  latter.  The  effect  of  grain  size  is  shown 
by  the  following  experiments: 1 

1  Ries,  Trans.  Amer.  Inst.  Min.  Engrs.,  Vol.  XXXIV,  p.  205,  1904. 


PHYSICAL  PROPERTIES  OF  CLAY  145 

A  white  clay  from  Georgia,  having  a  fusion-point  equal  to  cone  35 
of  the  Seger  series,  was  made  up  into  a  series  of  mixtures  with  other 
minerals.  One  set  of  mixtures  consisted  of: 

A.  Equal  parts  of  clay  and  hornblende,   the  latter  being  ground 
to  pass  a  150-mesh  sieve. 

B.  The  same  as  A,  the  hornblende  passing  through  a  100-mesh  sieve 
and  stopping  on  a  150-mesh. 

C.  The  same  as  A,  but  the  hornblende  ground  to  pass  an  80-mesh, 
but  retained  on  a  100-mesh. 

When  burned  to  cone  5  the  three  were  little  affected,  except  that 
the  one  with  the  finest  grains  was  colored  uniformly  red,  while  that 
with  the  coarsest  grains  presented  a  speckled  appearance.  When 
burned  to  cone  8  the  bar  of  mixture  A  was  considerably  bent  at  both 
ends,  while  that  of  B  was  nearly  straight,  and  C  was  perfectly  straight- 
At  cone  10,  B  was  thoroughly  fused  and  C  slightly  bent. 

This  seemed  to  show  well  the  effect  of  grain  size  in  the  case  of  horn- 
blende. The  object  of  taking  such  a  large  amount  of  fluxing  material 
was  simply  to  get  results  at  moderate  temperatures.  A  second  simi- 
lar set  of  mixtures,  containing  calcite  in  place  of  hornblende,  gave  simi 
lar  results. 

Condition  of  oxidation. — Finally  it  is  found  that  the  same  clay 
will  fuse  at  a  lower  temperature,  if  in  burning  it  is  deprived  of  oxygen, 
than  it  will  if  burned  in  an  atmosphere  containing  plenty  of  the  latter. 

Expression  of  fusibility. — Several  investigators  have  aimed  to 
express  the  fusibility  of  a  clay  by  means  of  a  formula  based  on  the 
relation  of  fluxes  to  refractory  elements,  fineness  of  grain,  or  density. 

Bischof 's  formula. — One  of  the  earliest  developed  was  that  of  Bischof l 
whose  expression  termed  the  Feuerfestigkeits-Quotient  is  as  follows: 

F  Q  _  (Oxygen  in  A1203)2 


(Oxygen  in  RO)  (Oxygen  in  SiO2)7 

in  which  RO  represents  the  sum  of  the  fluxes,  each  considered  as  the 
protoxid.  The  F.Q.  may  range  from  a  small  decimal  to  25. 

It  will  be  seen  from  this  formula  that  the  fusibility  of  clays  varies 
directly  as  the  square  of  the  oxygen  in  the  alumina,  and  inversely  as 
the  oxygen  in  the  fluxes  and  silica,  and  Bischof  concluded  that  the 
amount  of  alumina  in  a  clay  practically  influenced  its  fusibility. 

Bischof,  on  the  basis  of  this  formula,  classified  fire-clays  into  seven 
types  or  groups,  in  which  the  most  refractory  has  a  value  for  F.Q. 

1  Die  feuerfesten  Thone,  p.  116. 


146  CLAYS 

of  14,  and  the  least  refractory  that  is  used  for  fire-brick  has  a  value 
of  1.6.  He  selected  seven  type  clays,  which  he  considered  representa- 
tive of  each  of  these  groups. 

The  objections  to  Bischofs  formula  have  been  clearly  stated  by 
Wheeler  1  as  follows  : 

"1.  That  while  an  increase  in  the  percentage  of  alumina  decreases 
the  fusibility,  when  it  becomes  very  high  it  acts  the  part  of  an  acid 
instead  of  a  base  and  tends  to  lower  the  fusing-point,  or  the  reverse 
of  Bischofs  formula  when  this  point  is  reached;  neither  does  the  fusi- 
bility decrease  when  the  alumina  is  in  moderate  amounts,  at  the  rapid 
rate  of  the  square  of  the  alumina. 

"  2.  When  the  silica  is  present  in  amounts  greater  than  a  mono- 
silicate  (which  is  always  the  case  with  clays),  the  fusibility  decreases 
as  the  silica  increases,  which  is  just  the  reverse  of  Bischofs  formula. 

"3.  As  a  broad  rule,  the  fusibility  increases  as  the  bases  increase, 
at  least  to  the  extent  that  they  occur  in  clays;  but  there  is  a  very  great 
range  of  fusibility  according  to  the  bases  that  are  present.  The  alka- 
lies are  more  readily  fusible  than  the  ferrous  oxide,  and  this  in  turn 
than  the  lime  or  magnesia.  Again  a  mixture  of  bases  is  more  fusible 
than  a  single  base,  and  the  greater  the  number  of  bases  the  greater 
the  fusibility.  Bischofs  formula,  however,  pays  no  attention  to  the 
bases  present,  or  the  number  of  them. 

"4.  Again  equal  weight  is  given  to  all  fluxes,  and  all  physical  factors 
are  ignored. 

Seger's  formula.  —  H.  Seger,2  recognizing  the  unsatisfactory  character 
of  Bischofs  formula,  suggested  the  following  substitute: 

(A1203)2      A1203 
'**'     ROXSiO2      R2O3' 

While  this  formula  gives  better  results,  it  likewise  neglects  porosity 
and  texture. 

Wheeler's  formula.  —  Wheeler  3  has  suggested  a  formula  for  expressing 
the  relation  between  the  detrimentals  and  non-detrimental  constituents 
of  a  clay,  which  he  terms  the  Fusibility  factor  It  is 

N 


1  Mo.  Geol.  Surv.,  Vol.  XI,  p.  146,  1896. 

2  Collected  Writings  of  Seger,  Translation,  I,  p.  486,  1902. 

3  Mo.  Geol.  Surv.,  Vol.  XI,  p.  149,  1896. 


PHYSICAL   PROPERTIES  OF  CLAY  147 

in  which  N  =  sum  of  total  silica,  alumina,  titanic  acid,  water,  and  car- 
bonic acid; 

I)  =  total  fluxes,  namely,  alkalies,  iron  oxide,  lime,  magnesia; 
D'  =  sum  of  alkalies. 

This  formula  makes  no  distinction  between  free  and  combined  silica 
and  assumes  that  silica  in  a  free  state  does  not  act  as  a  flux.  The  alkalies 
are  added  twice,  because  of  their  supposed  greater  fluxing  power.  This 
formula  is  applicable  however  only  to  clays  which  are  physically  alike. 

For  those  of  differing  physical  properties  Wheeler  suggests  the  fusi- 
bility factor 

N 


F.F.= 


D  +  D'  +  C" 


C  having  these  values:  C  =  l   when  clay  is  coarse  grained  and  specific 

gravity  exceeds  2.25; 
C  =  2  when  clay  is  coarse  grained  and  specific 

gravity  ranges  from  2  to  2.25; 
C  =  3  when  clay  is  coarse  grained  and  specific 

gravity   ranges   from    1.75  to  2.00; 
C  =  2  when    clay   is    fine   grained    and    specific 

gravity  is  over  2.25; 
C  =  3   when    clay   is   fine   grained    and    specific 

gravity  is  from  2  to  2.25; 
C  =  4  when   clay  is    fine   grained   and    specific 

gravity  is  from  1.75  to  2.25. 

While  this  formula  is  a  step  in  the  right  direction,  it  is  not  altogether 
satisfactory,  as,  for  example,  the  values  are  not  specific  because  there  is 
no  accurate  method  of  expressing  the  fineness.  Moreover,  the  specific 
gravity  is  not  the  true  specific  gravity. 

There  is,  after  all,  some  question  in  the  author's  mind  whether  a 
formula  involving  the  necessity  of  at  least  a  chemical  analysis  and 
specific-gravity  determination  is  any  more  valuable  than  a  statement 
of  the  actual  temperature  or  cone  of  fusion. 

Methods  of  Measuring  Fusibility 

The  methods  used  for  measuring  the  fusibility  of  clays  may  be  divided 
into  two  classes,  namely,  the  direct  and  indirect. 

Direct  methods. — The  temperature  at  which  a  clay  fuses  is  determined 
either  by  means  of  test-pieces  of  known  composition  or  by  some  form 
of  apparatus  or  mechanical  pyrometer,  the  principle  of  which  depends 


148  CLAYS 

on  the  expansion  of  gases  or  solids,  thermoelectricity,  spectrophotometry, 
etc. 

While  there  are  many  different  forms  of  these  on  the  market  a  few 
only,  especially  those  which  have  been  most  commonly  used,  need  be 
described. 

Seger  cones. — These  test-pieces  consist  of  a  series  of  mixtures  of 
clays  with  fluxes,  so  graded  that  they  represent  a  series  of  fusion-points, 
each  being  but  a  few  degrees  higher  than  the  one  next  to  it.  They  are 
so  called  because  originally  introduced  by  H.  Seger,  a  German  ceramist. 
The  materials  which  he  used  in  making  them  were  such  as  would  have 
a  constant  composition,  and  consisted  of  washed  Zettlitz  kaolin,  Rorstrand 
feldspar,  Norwegian  quartz,  Carrara  marble,  and  pure  ferric  oxide. 
Cone  1  melts  at  the  same  temperature  as  an  alloy  composed  of  one 
part  of  platinum  and  nine  parts  of  gold,  or  at  1150°  C.  (2102°  F.).  Cone 


FIG.  34. — Seger  cones  used  for  determining  heat  effects  in  kilns.  Nos.  7  and  8 
were  completely  melted;  No.  10  was  slightly  softened;  No.  12  was  unaffected; 
No.  9  was  bent  completely  over,  but  not  melted.  The  fusing-point  of  cone  9 
was  reached. 

20  melts  at  the  highest  temperature  obtained  in  a  porcelain  furnace, 
or  at  1530°  C.  (2786°  F.).  The  difference  between  any  two  successive 
numbers  is  20°  C.  (36°  F.),  and  the  upperjnember  of  the  series  is  cone  39. 
Cone  36  is  composed  of  a  very  refractory  clay  slate,  while  cone  35  is 
composed  of  kaolin  from  Zettlitz,  Bohemia.  A  lower  series  of  numbers 
was  produced  by  Cramer,  of  Berlin,  who  mixed  boracic  acid  with  the 
materials  already  mentioned.  Hecht  obtained  still  more  fusible  mixtures 
by  adding  both  boracic  acid  and  lead  in  proper  proportions  to  the  cones. 
The  result  is  that  there  is  now  a  series  of  61  numbers,  the  fusion-point 
of  the  lowest  being  590°  C.  (1094°  F.)  and  that  of  the  highest  1940°  C. 


PHYSICAL  PROPERTIES  OF  CLAY  149 

(3470°  F.).  As  the  temperature  rises  the  cone  begins  to  soften,  and 
when  its  fusion-point  is  reached  it  begins  to  bend  over  until  its  tip  touches 
the  base  (Fig.  34).  For  practical  purposes  these  cones  are  very  successful, 
though  their  use  has  been  somewhat  unreasonably  discouraged  by 
some.  They  have  been  much  used  by  foreign  manufacturers  of  clay 
products  and  their  use  in  the  United  States  is  increasing. 

The  composition  and  fusing-points  of  the  different  members  of  the 
series  are  given  below  : 

COMPOSITION  AND  FUSING-POINTS  OF  SEGER  CONES 

*°n°f  Composition.  o-Furin*.point^ 

022     $0.5Na20)  J2.0     SiO2)  '  ' 

•°22     )0.5   PbO}  ..............  Jl.  0    B2OJ  ............     I'09 

021      $0.5Na20)     01     A1Q       \2.2     SiOJ 
•°21     )0.5   PbO)     °'1     Ai2°3     )1.0    B203j  ............       ' 


)  02  A1Q  J2.4  SiOJ 

JO.  5   PbO)  U'^  Ai*Ua  \l.Q  B2O3J  ............  1'2()2 

JO-.5Na20)  03  A10  >2'6  Si°2)  1256  fiRO 

)0.5   PbO)  0*a  AlaUs  ^1.0  B2O3)  ............  1>Z5b 


.2          Q4     A10       ^2.8     SiO2)  13 

Al2Us     H-0    B2O3J  ............     i>61 


O.  5   PbO)       '  23     H-0    B20 


.a2  Afi^AlO  - 

014     JO.  5   PbOj  °'6£>  Ai2°3  H-0  B203 

^0.5Na9O)  n?     A10  ^3.4  SiO2 

013  jo.5  Pboi  °-7  A1?°3  no  B2o3 


,10         .a2)  ft  7r.  A10  ^3.5  SiO2 

012     JO.  5   Pbol  °  '5  Ai2°3  U-0  B203 

^0.5Na2O^  ft8  A,  0  ^3.6  SiO2 

011     JO.  5   PbO^  Ala°3  H-0  B203 


OQ       ^0.3    K20)     0.2     Fe203     J3.55  SiO2)  x  778 

09       JO.  7    CaO^     0.3     A1203     )0.45  B2O3)  ..... 


^0.3    K20)     0.2     Fe203     ^3.60  SiO2) 
08       JO.  7    CaOi     0.3     A1203     ^0.40  B2O3^ 


0.3    K2O)     0.2     Fe2O3     ^3.75 
O.  7    Caol     0.3     Al20b 


? 
770 


.a.2)     nfi     A10      }3.2     SiO2)  ,  472 

015     JO.  5   PbOJ  Al2°3     H-0    B203J  ............     lj47 


0.2     Fe203     ^3.50  SiO2)  x  742  95Q 

0.3     A1203     J0.50  B2OJ  ............     *'74 


__       J0.3  K2O)  0.2  Fe2O3  ^3.65  SiO2)  1  850  , 

°7       JO.  7  CaOi  0.3  A1203  )0.35  B2O3)  ............ 

^0.3  K2O)  0.2  Fe203  ^3.70  SiO2)  1  886  , 

°6       JO.  7  CaO^  0.3  A1203  J0.30  B2O3(  ............ 


150  CLAYS 

COMPOSITION  AND  FUSING-POINTS  OF  SEGER  CONES — (Continued) 

No.  of                                                                   Composition.  0-^nS-P<>int.^ 

Cone.  *•  V1 

)0.3  K20)     0.2     Fe203     J3.8Q   SiOJ  ,  gr-8              1 070 

•°4       JO. 7  CaOJ     0.3     A1203     )0.20  B2O3J ^ 

nq       }0.3  K20)     0.2     Fe,03     ^3.85  SiO2)  l  g94              1 090 

•°3       JO. 7  do\     0.3     A1203     ^0.15B203^ 1)9J                1)U9 


)0.3    K20)     0.2     Fe203     J3.90  SiO2) 
0.3     A1203     J0.10  B2O3^ 

Si  S8    S:S 


Si 


J0.3   K,O)     0.05  Fe203     }4  SiQ  2174 

3  J0.7    CaOS     0.45  A12O3     }4     lUa 2'1/4 


4             !n'?  n~2nl     °-5    Al2O34SiO2 2,210  1,210 

^  U .  i  UaL> ) 

5      |2:?  &8|  °-5  A1'°35Si°2 2'246  i'230 

6  |g'|  ^Q]     0.6    Al2036Si02..' 2,282  1,250 

7  ]^;3  ^3]     0.7    Al2037Si02 2,318  1,270 

8  )^;3  ^g]     0.8    Al2038Si02 2,354  1,290 


9  07    nQ2X!     °-9    Al2O39SiO2 2,390  1,310 


10  '7  Q  1.0    Al20310Si02  ......  .......  .......  2,426  1,330 

?  CaOJ  1>2    A12°312Si°2  ....................  2>462  1,350 

12  '|  ^Q]  1.4    Al20314Si02.  ...................  2,498  1,370 

13  JQ-J  CaOJ  1>6    A120316Si02  ....................  2,534  1,390 

14  )o!7  CaOJ  1-8    Al20318Si02  ....................  2,570  ,1,410 

15  |{5;|  §JQJ  2.1    Al20321SiO?  ....................  2,606  1,430 

16  |o!7  Ca'oj  2'4    A12°324Si02  ....................  2,642  1,450 

17  |g'J  §g|  2.7    Al20327Si02  ....................  2,678  1,470 

18  |g'J  gjgj  3.1    Al2033lSi02  ....................  2,714  1,490 

19  |o!7  CaOJ  3'5   A120335Si02  ....................  2,750  1,510 


PHYSICAL   PROPERTIES  OF  CLAY                             151 

COMPOSITION 

AND    FU8ING-POINTS 

OF  SEGER  CONES  —  (Continued) 

Composition. 

'-Fusing-point.— 
0  F  .                    °  C. 

$0.3    K2O| 
)0.7    CaO$ 

3.9    Al,O339SiO2 

2,786 

1.530 

$0.3    K.,0) 
(0.7    CaO$ 

4.4    Al2O344SiO2 

2,822 

1,550 

$0.3    K2O) 
)0.7    CaO$ 

4.9    Al,O349SiO2 

2,858 

1,570 

$0.3    K.,0) 
JO.  7    CaO$ 

5.4    Al,O354SiO2. 

2,894 

1,590 

$0.3    K20) 
}0.7    CaO$ 

6.0    Al,O,60SiO2    , 

2,930 

1,610 

$0.3    K,O) 
)0.7    CaO$ 

6.6    Al,O366SiO2.  .  , 

2,966 

1,630 

$0.3    K20) 
JO.  7    CaO$ 

7.2    Al2O372SiO2 

3,002 

1,650 

}0\7    CaO$ 

20      Al.,O3200SiO2 

3,038 

1,670 

A12O3    10 

SiO,    

3,074 

1,690 

A12O3      8 

SiO?    

3,110 

1,710 

A12O3      6 

SiO,    

3,146 

1,730 

A120,      5 

SiO,    

3,182 

1,750 

A12O3      4 

SiO,    

3,218 

1,770 

A12O3      3 

SiO,    

3,254 

1,790 

A12O3      2.5 

SiO,    

3,290 

1,810 

A12O3      2 

Si02    

3,326 

1,830 

A1203      1.5 

SiO2    

3,362 

1,850 

3,398 

1,880 



3  434 

L910 



3,470 

1,940 

No.  of 
Cone. 

20 
21 
22 
23 
24 
25 
26 

27 

28 
29 
30 
31 
32 
33 
34 
35 
36 
37 
38 
39 

In  actual  use  they  are  placed  in  the  kiln  at  a  point  where  they  can 
be  watched  through  a  peep-hole  (Fig.  35),  but  at  the  same  time  will 
not  receive  the  direct  touch  of  the  flame  from  the  fuel.  It  is  always 
well  to  put  two  or  more  cones  of  different  .numbers  in  the  kiln,  so  that 
warning  can  be  had,  not  only  of  the  end  point  of  firing  but  also  of  the 
rapidity  with  which  the  temperature  is  rising. 

In  determining  the  proper  cone  to  use  in  burning  any  kind  of  ware, 
several  cones  are  put  in  the  kiln,  as,  for  example,  numbers  .08,  1  and  5. 
If  .08  and  1  are  bent  over  in  burning  and  5  is  not  affected  the  tem- 
perature of  the  kiln  is  between  J  and  5.  The  next  time  numbers  2, 
3,  and  4  are  put  in,  and  2  and  3  may  be  fused,  but  4  remains  unaffected, 
indicating  that  the  temperature  reached  the  fusing-point  of  3. 

While  the  temperature  of  fusion  of  each  cone  is  given  in  the  pre- 
ceding table,  it  must  not  be  understood  that  these  cones  are  for  measur- 


152  CLAYS 

ing  temperature,  but  rather  for  measuring  pyrochemical  effects.  Thus 
if  certain  changes  are  produced  in  a  clay  at  the  fusing-point  of  cone  5, 
the  same  changes  can  be  reproduced  at  the  fusion-point  of  this  cone, 
although  the  actual  temperature  of  fusion  may  vary  somewhat,  due 
to  variation  in  the  condition  of  the  kiln  atmosphere.  As  a  matter  of 
fact,  however,  repeated  tests  with  a  thermoelectric  pyrometer  demon- 
strate that  the  cones  commonly  fuse  close  to  the  theoretic  temperatures. 
Manufacturers  occasionally  claim  that  the  cones  are  unreliable  and 
not  satisfactory,  forgetting  that  their  misuse  may  often  be  the  true 


FIG.  35. — Section  of  kiln  showing  method  of  placing  Seger  cones. 

reason  for  irregularities  in  their  behavior.  It  is  unnecessary,  perhaps, 
to  state  that  certain  reasonable  precautions  should  be  taken  in  using 
these  test-pieces.  The  cones  are  commonly  fastened  to  a  brick  with 
a  piece  of  wet  clay,  and  should  be  set  in  a  vertical  position.  After 
being  placed  in  a  position  where  they  can  be  easily  seen  through  a  peep- 
hole, the  latter  should  not  be  opened  widely  during  the  burning,  lest 
a  cold  draft  strike  the  cones,  and  a  skin  form  on  its  surface  and  inter- 
fere with  its  bending.  If  the  heat  is  raised  too  rapidly,  the  cones  which 
contain  much  iron  swell  and  blister  and  do  not  bend  over,  so  that  the 
best  results  are  obtained  by  the  slow  softening  of  the  cone  under  a 
gradually  rising  temperature.  Aside  from  this,  however,  trouble  has 
been  experienced  with  cones  Nos.  010  to  3,  which  may  act  irregularly 


PHYSICAL   PROPERTIES   OF  CLAY  153 

if  exposed  for  any  length  of  time  to  sulphurous  fumes  from  the  fuel, 
as  in  burning  in  some  muffle-kilns,  where  there  is  not  a  free  circula- 
tion of  air  in  the  muffle.  The  sulphuric  acid  appears  to  cause  a  vola- 
tilization of  the  boracic  acid,  and  unite  with  the  lime  in  the  exterior 
of  the  cone,  forming  a  hard  skin  of  less  fusible  character  than  the  interior; 
which  melts  while  the  outside  is  still  hard.  It  has  been  suggested  that 
the  composition  of  these  members  of  the  cone  series  be  changed.1  One 
set  of  cones  cannot  be  used  to  regulate  an  entire  kiln,  but  several  sets 
should  be  placed  in  different  portions  of  the  same.  One  advantage 
possessed  by  a  cone  over  trial-pieces  is  that  the  cone  can  be  watched 
through  a  small  peep-hole,  while  a  larger  opening  must  be  made  to  draw 
out  the  trial-pieces.  If  the  cones  are  heated  too  rapidly,  those  con- 
taining a  large  percentage  of  iron  are  apt  to  blister. 

Zimmer2  has  pointed  out  that  with  slow  firing  in  a  large  biscuit- 
kiln  the  cones  1-9  reached  a  melting-point  of  25°  to  30°  C.  lower  than 
those  placed  in  a  small  trial-kiln,  whose  temperature  increased  faster, 
but  since  it  is  heat  effects  and  not  degrees  of  temperature  that  we  are 
measuring,  this  makes  no  difference. 

The  cone  numbers  used  in  the  different  branches  of  the  clay-work- 
ing industry  in  the  United  States  are  approximately  as  follows: 

Common  brick 012-01 

Hard-burned,  common  brick 1-2 

Buff  front  brick 5-9 

Hollow  blocks  and  fireproofing 03-  1 

Terra  cotta 02-  7 

Conduits 7-8 

White  earthenware 8-9 

Fire  bricks 5-18 

Porcelain 11-13 

Red  earthenware 010-05 

Stoneware 6-  8 

Thermoelectric  pyrometer. — This  pyrometer  is  one  of  the  best 
instruments  for  measuring  temperatures.  It  is  based  on  the  principle 
of  generating  an  electric  current  by  the  heating  of  a  thermopile  or  ther- 
moelectric couple  consisting  of  two  wires,  one  of  platinum  and  the 
other  of  an  alloy  of  90  per  cent  platinum  and  10  per  cent  rhodium. 
These  two  are  fastened  together  at  one  end,  while  the  two  free  ends 
are  carried  to  a  galvanometer  which  measures  the  intensity  of  the  cur- 
rent. That  portion  of  the  wires  which  is  inserted  into  the  furnace  or 

1  Trans.  Amer.  Cer.  Soc.,  Vol.  II,  p.  60,  and  III,  p.  180. 

2  Ibid.,  Vol.  I,  p.  23. 


154  CLAYS   . 

kiln  is  placed  within  two  porcelain  tubes,  one  of  the  latter  being  smaller 
and  sliding  within  the  other  in  order  to  insulate  the  wires  from  each 
other.  The  larger  tube  has  a  closed  end  to  protect  the  wires  from  the 
action  of  the  fire-gases.  The  shortest  tubes  put  on  the  market  are 
about  15  inches  long,  while  the  longest  are  54  inches. 

To  measure  the  temperature  of  a  furnace  or  kiln  the  tube  containing 
the  wires  is  placed  in  it  either  before  starting  the  fire,  or  else  during 
the  burning.  If  the  latter  method  is  adopted,  the  tube  must  be  intro- 
duced very  slowly,  to  prevent  its  being  cracked  by  sudden  heating. 
The  degrees  of  temperature  are  measured  by  the  amount  of  deflection 
of  the  needle  of  the  galvanometer. 

Thermoelectric  pyrometers  are  useful  for  measuring  the  rate  at 
which  the  temperature  of  a  kiln  is  rising,  or  for  detecting  fluctuations 
in  the  same.  It  is  not  necessary  to  place  the  galvanometer  near  the 
kiln,  for  it  can  be  kept  in  the  office  some  rods  away.  This  pyrometer 
is  not  to  be  used  as  a  substitute  for  Seger  cones;  but  to  supplement  them 
The  more  modern  forms  have  an  automatic  recording-device.  As  at 
present  put  on  the  market  the  thermoelectric  pyrometer  costs  about 
$180,  and  the  price,  delicacy  of  the  instrument,  and  lack  of  realiza- 
tion of  its  importance  have  all  tended  to  restrict  its  use.  However, 
many  of  the  larger  clay-working  plants  are  adopting  it,  as  it  is  better 
than  other  forms  of  pyrometer  for  general  use  and  probably  more  accu- 
rate. It  can  be  used  up  to  1600°  C.  (2912°  F.). 

Wedgewood  pyrometer. — This  pyrometer,  which  has  been  used 
from  time  to  time  in  ceramic  establishments,  depends  on  the  shrinkage 
of  clay  cylinders,  whose  contraction  is  supposed  to  be  proportionate  to 
the  temperature  to  which  they  are  exposed.  Their  behavior  is  unreliable. 

Lunette  optical  pyrometer. — This  consists  of  a  small  telescope  con- 
taining a  quartz  plate  between  two  Nicol  prisms.  When  looking  at  a 
heatod  body  through  it  one  of  the  prisms  is  revolved  until  the  red  color 
changes  to  yellow,  then  green,  and  lastly  blue.  The  angle  of  rotation 
necessary  to  extinguish  the  red  is  measured,  and  the  temperature  deter- 
mined by  this  means.  It  is  only  approximate  in  its  recording  action 
and  rather  unsatisfactory  in  its  work. 

Classification  of  clays  based  on  fusibility.1 — The  fact  that  different 
clays  fuse  at  different  temperatures  makes  it  possible  to  divide  them 
into  several  different  groups,  the  divisions  being  based  on  the  degree 
of  refractoriness  of  the  material.  Such  a  grouping,  however,  is  more 
or  less  arbitrary,  since  no  sharp  natural  lines  can  be  drawn  between 
the  different  groups,  and  it  is  to  be  expected  that  no  grouping  pro- 

1  N.  J.  Geol.  Surv.,  Fin.  Kept.,  VI,  p.  100. 


PHYSICAL  PROPERTIES  OF  CLAY  155 

posed  will  meet  with  universal  approval.     The  following  classification 
was  adopted  by  the  author  in  studying  the  New  Jersey  fire-clays: 

1.  Highly  refractory  clays,  those  whose  fusing-point  is  above  cone  33. 
Only  the  best  of  the  so-called  No.  1  fire-clays  belong  to  this  class. 

2.  Refractory  clays,  those  whose  fusion-point  ranges  from  cone  31- 
33  inclusive.     This  group  includes  some  of   the  New  Jersey  No.  1,  as 
well  as  some  No.  2  fire-clays. 

3.  Semi-refractory    clays,    those    whose    fusion-point    lies    between 
cones  27  and  30  inclusive. 

4.  Clays  of  low  refractoriness,  those  whose  fusion-point  lies  between 
cones  20  and  26  inclusive. 

5.  Non-refractory  clays,  fusing  below  cone  20. 

Indirect  methods. — There  are  several  indirect  methods  of  deter- 
mining temperatures,  but  that  of  Bischof  1  is  perhaps  the  best  known. 
This  consists  in  increasing  the  refractoriness  of  weighed  samples  by 
adding  to  them  increasing  quantities  of  an  intimate  mixture  of  equal 
parts  of  chemically  pure  silica  and  alumina,  and  heating  them  with  a 
prism  of  Saarau  fire-clay  (whose  fusing-point  is  Seger  cone  36)  to  above 
the  melting-point  of  wrought  iron.  The  amount  of  the  mixture  required 
to  tone  the  clay  up  to  the  same  refractoriness  as  the  standard  indi. 
cates  its  quality.  It  was  used  by  Bischof  chiefly  for  refractory  clays- 

Hofman  and  Demond  2  tried  the  method  of  mixing  various  samples 
of  fire-clays  with  varying  proportions  of  calcium  carbonate,  and  cal- 
cium carbonate  and  silica,  to  render  them  fusible  at  temperatures 
below  the  melting-point  of  platinum,  while  common  brick-clays  were 
mixed  with  alumina  and  silica  to  decrease  their  fusibility,  the  object 
being  to  arrive  at  a  standard  temperature  at  which  both  refractory 
and  fusible  clays  could  be  tested.  The  results  obtained  at  first  were 
very  satisfactory,  but  subsequent  ones  did  not  result  as  was  desirep 
and  the  method  had  to  be  abandoned. 

More  recently,  however,  this  method  has  been  tried  by  J.  L.  Newell 
and  G.  A.  Rockwell  with  much  better  results.3  In  these  last  experi- 
ments the  Seger  cone  26  was  used  as  a  standard,  as  it  was  regarded  as 
forming  the  line  between  refractory  and  non-refractory  clays,  the  non- 
refractory  ones  being  toned  up  until  they  showed  the  same  behavior 
in  the  fire  as  cone  26.  The  amount  of  toner  added  then  gave  an  idea 
how  far  the  clay  stood  below  the  lower  limit  of  refractoriness. 

The  silica  used  in  the  experiments  was  quartz,  ground  to  pass  a 

1  Dingler's  Polyt.  Jour.,  Vol.  CXCVI,  pp.  438,  525,  and  CXCVIII,  p.  396. 

2  Trans.  Amer.  Inst.  Min.  Engrs.,  XXV,  p.  3,  1896. 

3  Ibid.,  XXVIII,  p.  435,  1899. 


156 


CLAYS 


100-mesh  sieve  and  purified  by  boiling  in  nitrohydrochloric  acid.  It 
had  99.88  per  cent  silica.  The  alumina  contained  98.48  A12O3. 

The  method  followed  was  to  weigh  out  samples  of  1  gram  of  the 
clay  to  be  tested  and  mix  them  severally  with  0.1,  0.2,  0.3,  etc.,  grams 
of  the  silica-alumina  mixture.  The  samples  were  then  tested  in  the 
Deville  furnace. 

The  following  table  gives  the  results  of  the  experiments  just  described, 
the  clays  being  arranged  in  the  order  of  their  refractoriness,  and  in 
each  case  the  amount  of  flux  being  given  that  was  required  to  raise 
the  fusing-point  to  that  of  cone  26  of  Seger. 

ANALYSES  OF  CLAYS  AND  RESULTS  OF  TESTS 


Sample  No. 

26  l 

25  1 

31 

22  ! 

241 

231 

19822 

SiO2               

Per  cent. 
64.10 

Per  cent. 
55.60 

Per  cent. 
57   10 

Per  cent. 
57  45 

Per  cent. 
57   15 

Per  cent. 
49   30 

Per  cent. 
43  94 

ALO, 

21.79 

24.34 

21   29 

21   06 

20  26 

24  00 

11   17 

H2O  comb  

6  05 

6.75 

6  00 

5  90 

5  50 

9  40 

3  90 

Total  

91.94 

86.69 

84  39 

84  41 

82  91 

82  70 

59  01 

Fe,O,  . 

2.51 

6.11 

7  31 

7  54 

7  54 

8  40 

3  81 

CaO 

0  10 

0  43 

0  29 

0  29 

0  90 

0  56 

11  64 

MgO 

0  58 

0  77 

1  53 

1  22 

1  6? 

1  60 

4  17 

K2O 

2  62 

3  00 

3  44 

3  27 

3  05 

3  91 

2  90 

Na2O                  

0  03 

0  09 

0  61 

0  39 

0  58 

0  17 

0  71 

Total          

5  84 

10  40 

13  18 

12  71 

13  69 

14  64 

23  23 

Moisture  

1  10 

2  65 

1  30 

1  90 

2  70 

1   20 

15  663 

Grand  total  

98  88 

99  74 

98  87 

99  02 

99  30 

98  54 

98  OO4 

Stiffening  ingredient,  % 

20 

40 

60 

80 

80 

100 

180 

1 N.  W.  Lord  anal.         2E.  Orton,  Jr.,  anal.         3Includes  CO2.         *  Includes  P2O5  0.10%. 


Changes  Taking  Place  in  Burning 

The  changes  which  occur  in  burning  are  of  two  kinds,  chemical 
and  physical,  the  two  being  more  or  less  closely  related;  in  fact  the 
physical  effects  are  often  the  results  of  chemical  changes. 

While  the  chemical  changes  are  much  the  same  for  all  clays,  still 
they  vary  greatly  in  degree.  The  temperature  at  which  many  of  these 
occur  is  also  fairly  constant,  but  may  be  influenced  somewhat  by  the 
composition  of  the  clay  and  the  fire-gases. 

The  changes  which  occur  in  burning  may  be  roughly  divided  into 
three  stages,  termed  the  periods  of  dehydration,  oxidation,  and  vitri- 


PHYSICAL  PROPERTIES   OF  CLAY  157 

fication,  each  of  which  are  characterized  by  certain  reactions,  but  there 
is  no  sharp  dividing-line  between  the  different  ones,  the  changes  of 
one  stage  beginning  before  those  of  the  preceding  stage  are  completed. 

Dehydration  period. — In  the  beginning  of  burning  the  last  traces 
of  moisture  are  driven  off.  This  vapor,  which  is  termed  water-smoke 
or  steam  by  the  brick-maker,  is  simply  the  moisture  which  has  been 
retained  in  the  pores  of  the  clay.  Its  expulsion  results  in  a  slight  loss 
of  weight.  The  driving  out  of  the  moisture  is  facilitated  by  raising 
the  heat  slowly,  and  by  allowing  sufficient  draft  to  pass  through  the 
kiln  in  which  the  clay  is  being  burned.  Raising  the  temperature  too 
fast  expels  the  steam  too  quickly  and  causes  a  popping  of  the  brick. 

On  the  other  hand,  a  stopping  or  retardation  of  the  draft  results 
in  a  saturation  of  the  kiln  atmosphere  with  moisture,  and  its  depo- 
sition on  the  surface  of  the  ware,  producing  the  effect  known  as 
"scumming"  or  " whitewashing."  This  is  caused  in  this  way:  All 
bituminous  coals  contain  some  sulphur,  which  on  burning  is  given 
off  in  the  form  of  sulphurous  gas,  and  is  then  absorbed  by  the  con- 
densed moisture  on  the  surface  of  the  ware.  The  acid  solution  thus 
formed  attacks  certain  salts  (especially  lime)  in  the  clay,  forming  soluble 
sulphates,  which  are  left  as  a  white  scum  on  the  surface  of  the  ware 
when  the  moisture  evaporates.  Sulphur  in  a  dry  atmosphere  would 
cause  but  little  harm.  It  is  therefore  desirable  to  use  a  fuel  for  dehy- 
dration which  contains  as  little  water  and  sulphur  as  possible.  This 
is  often  a  difficult  matter,  for  most  soft  coal  has  much  of  both,  and 
wood  contains  water.  Coke  and  charcoal  are  good,  but  their  use  is 
not  always  economically  practicable. 

From  the  point  at  which  the  water  evaporates,  up  to  450°  C.  (842°  F.), 
there  is  practically  no  change,  unless  gypsum  is  present,  and  this  will 
lose  most  of  its  chemically  combined  water  between  300°  C.  (572°  F.) 
and  400°  C.  (762°  F.).  The  amount  of  loss  in  this  manner  is  usually 
£0  small  as  to  be  negligible,  but  at  this  point  the  expulsion  of  the  chemi- 
cally combined  water  begins  and  is  practically  complete  by  700°  C. 
(1292°  F.),  that  is,  it  begins  at  a  very  dull  red  and  is  completed  at  a 
bright-red  heat. 

Before  the  dehydration  of  the  water  is  completed,  however,  other 
gases  begin  to  pass  off,  including  CO2  from  lime  and  iron  carbonates, 
sulphur  from  pyrite,1  and  gases  produced  by  the  combustion  of  carbon- 
aceous matter  in  the  clay,  but  all  of  these  may  not  have  passed  off 
after  the  dehydration  of  the  clay  is  ended.  Moreover  the  expulsion 

1  Pyrite  loses  only  a  portion  of  its  sulphur  at  this  temperature,  the  vbalance 
passing  off  later. 


158  CLAYS 

of  some  of  them  requires  the  presence  of  oxygen,  so  that  the  periods 
of  dehydration  and  oxidation  overlap. 

Oxidation  period. — In  the  oxidation  process,  which  may  begin 
at  a  comparatively  low  temperature,  as  low  as  500°  C.  (932°  F.),  and 
is  probably  completed  by  900°  C.  (1652°  F.),  the  following  changes 
take  place: 

1.  The  oxidation  or  burning  off  of  the  combustible  matter. 

2.  The  expulsion  of  the  remaining  sulphur  from  pyrite. 

3.  The  driving  off  of  carbon  dioxide. 

4.  The  oxidation  of  any  ferrous  iron  to  the  ferric  condition. 
Two  things  should  be  borne  in  mind  in  this  connection: 

1.  Oxidation  may  be  accomplished  without  the  aid  of  heat,  the 
process  going  on  slowly  when  the  clay  is  exposed  to  the  weather:     In 
this  case  both  FeS2  and  FeCOs  may  be  changed  to  the  oxide,  and  even 
organic  matter  may  be  partly  eliminated. 

2.  The  porosity  of  the  clay  materially  affects  the  process,  a  loose, 
open-textured  clay  allowing  these  changes  to  take  place  more  readily 
than   a   close-textured,   fine-grained   one,  which   retards   the   entrance 
of  the  oxidizing  gases  into  the  mass.      Grog   is  sometimes  added  to 
open  the  grain. 

From  this  we  can  see  that  the  presence  of  much  air  mixed  with 
the  fuel-gases  facilitates  the  removal  of  combustible  elements  in  the 
clay,  especially  organic  matter.  Since  air  carrying  oxygen  is  necessary 
to  help  in  removing  them,  it  follows  that  the  clay  must  be  sufficiently 
porous  to  allow  the  air  to  penetrate  it.  Now  if  the  expulsion  of  the 
water  in  the  clay  is  retarded,  thereby  keeping  the  pores  of  the  clay 
more  or  less  closed  up,  it  may  retard  the  expulsion  of  other  gases,  some 
of  which  may  be  retained  in  the  clay,  until  the  rising  temperature  has. 
sealed  up  the  pores  by  vitrification.  Thus  imprisoned,  and  subjected 
to  a  rising  temperature,  they  may  by  expansion  bloat  the  ware.  As 
pointed  out  by  Beyer  and  Williams,1  it  is  not  definitely  known  what 
gases  become  thus  imprisoned,  but  they  may  be  C02,  or  S02,  and  some 
have  suggested  that  oxygen  liberated  by  the  reduction  of  iron  to  the 
ferrous  condition  may  also  aid  in  bloating  or  blistering  the  ware. 

In  burning  bricks,  for  example,  if  the  ware  is  raised  to  a  vitrifying 
heat  before  oxidation  is  complete,  the  iron  in  the  central  part  of  the 
mass  remains  in  a  ferrous  condition,  forms  a  black  core,  which  if  the 
heating  continues  becomes  slaggy.  Any  imprisoned  carbonaceous  matter 
will  become  finally  decomposed,  and  the  expanding  gases  swell  up  tha 
clay  in  their  efforts  to  escape. 

1  la.  Geol.  Surv.,  XIV,  p.  278,  1904. 


PHYSICAL   PROPERTIES  OF  CLAY  159 

During  the  temperature  interval  in  which  dehydration  and  oxida- 
tion occur  there  are  few  or  no  reactions  going  on  between  the  clay 
particles,  but  as  the  temperature  of  vitrification  is  approached  chemi- 
cal union  occurs  between  the  different  minerals  in  the  clay,  and  as  it- 
goes  on  involves  an  increasing  number  of  elements  in  the  reactions, 
which  become  exceedingly  complex. 

The  clay,  if  red-burning,  will  show  a  much  brighter  color  at  the  end 
of  the  oxidation  period. 

Vitrification  period. — In  this  stage  texture  plays  an  important  role 
(see  under  Fusibility),  for  in  finer-grained  clays  chemical  reactions 
are  more  wide-spread  and  take  place  more  easily  than  in  coarse-grained 
ones.  Increasing  density  of  the  clay  and  increasing  homogeneity  of 
the  mass  produce  similar  effects. 

These  chemical  reactions  result  in  the  formation  of  silicates  of  ex- 
ceedingly complex  character. 

The  temperature  of  vitrification  is  exceedingly  variable,  being  as 
low  as  900°  C.  (1652°  F.)  or  1000°  C.  (1832°  F.)  in  some  clays,  while 
in  others  it  may  be  1200°  C.  (2192°  F.)  or  even  higher. 

After  the  clay  is  completely  vitrified  a  further  rise  of  temperature 
causes  it  to  swell,  soften  still  more,  and  finally  run. 

We  may  therefore  summarize  the  effects  of  heating  as  follows: 

1.  Loss  of  volatile  substances  present,  such  as  water,  carbon  dioxide, 
and  sulphur  trioxide,  the  volatilization  of  these  leaving  the  clay  more 
or  less  porous. 

2.  Oxidation    of     ferrous     to     ferric     compounds,    if     oxygen     is 
present. 

3.  A  shrinkage  of  the  mass,  by  further  heating. 

4.  Hardening  of  the  clay  due  to  fusion  of  some,  at  least,  of  tn« 
particles. 

5.  Increasing  density  with  rising  temperature,  the  maximum  being 
reached  at  the  vitrifying  point  of  the  clay. 

6.  Complete  softening  of  the  mass. 

Effects  due  to  variation  in  the  clay. — Burned  clays  may  be  of  many 
different  colors.  Although  the  majority  of  clays  contain  sufficient 
iron  oxide  to  burn  red,  nevertheless  it  is  not  safe  to  predict,  from  the 
color  of  the  raw  clay,  the  shade  that  it  will  burn,  since  some  bright 
red  or  yellow  clays  may  yield  a  buff  brick.  If  considerable  iron  oxide 
is  present,  4  to  5  per  cent,  the  brick  usually  burns  red,  unless  much  lime 
or  alumina  is  also  present.  If  only  2  to  3  per  cent  or  under,  the  clay  may- 
burn  white  or  buff.  An  excess  of  lime  in  the  clay  will,  however,  counter- 
act the  effect  of  the  iron  oxide  and  yield  a  buff  brick,  but  a  brick  owing 


160 


CLAYS 


its  buff   color  to  this  cause  will  not  stand  as  much  fire  as  one  which 
owes  its  buff  color  simply  to  a  low  percentage  of  iron  oxide. 

Where  a  clay  is  mottled,  as  red  and  white  for  instance,  the  colors 
of  the  different  spots  will  retain  their  individuality  most  plainly  after 
burning,  unless  the  clay  is  thoroughly  mixed.  Many  clays  contain 
lumps  of  whitish  clay,  much  tougher  than  the  rest  of  the  mass.  These 
resist  disintegration  in  the  tempering-machines,  so  that  after  burning 
they  can  be  plainly  seen,  as  white  spots  in  the  red  ground  of  the  brick. 

ANALYSES  SHOWING  DIFFERENCE  BETWEEN  RAW  AND  BURNED  CLAY 


I. 

II. 

III. 

IV. 

V. 

VI, 

VII. 

Silica  (SiO2)  
Alumina  (A12O3)  
Ferric  oxide  (Fe2O3).  .  . 
Lime  (CaO)  
Magnesia  (MgO)  
Potash  (K  O) 

74.03 
17.10 
.57 
.10 
22 
.'30 
.60 

1.36 
6.15 

78.5 
21.3 
tr. 

.5 
.3 

with 
A1203 
none 

74.04 
15.15 
.50 
.50 
.27 
.42 
1.12 

1.31 
6.00 

73.94 

20.47 
1.80 
1.08 
1.16 
.61 
.64 

.83 

49.45 
17.11 
3.45 
12.67 
1.77 
.13 
.21 

.70 
4.84 
7.10 
2.00 

56.6 
20.4 
6.2 
11.7 
1.4 
1.5 
1.4 

with 
A1203 
.5 
none 
none 
none 

56.5 
20.2 
6.1 
11.6 
1.8 
1.5 
1.3 

with 
A12O3 
none 
none 
none 
none 

99.1 

Soda  (Na  O) 

Titanium  oxide  (TiO2). 
Water  (H2O)  

Carbon  dioxide  (CO2).  .  . 
Sulphur  trioxide  (SO3).  . 
P  errous  oxide  

Total  

100.43 

101.1 

99.31 

100  .  53 

99.43 

99.7 

Total  fluxes  

1.79 

2.81 

5.27 

18.23 

I.  Fire-clay  from  six  miles  southeast  of  Sulphur  Springs,  Tex.     O.  H.  Palm,  analyst. 
II.  Brick  from  same.     S.  H.  Worrell,  analyst. 

III.  Fire-clay,  Athens,  Tex.     O.  H.  Palm,  analyst. 

IV.  Fire-brick,  Athens,  Tex.     O.  H.  Palm,  analyst. 
V.  Brick  shale,  Ferris,  Tex.     O.  H.  Palm,  analyst. 

VI    Brick  from  same.     O.  H.  Palm,  analyst. 
VII.  Hard-burned  brick.     O.  H.  Palm,  analyst. 

The  normal  iron  coloration  may  often  be  destroyed  by  the  effects 
of  the  fire-gases.  When  these  are  reducing  in  their  action  (i.e.,  taking 
a  part  of  the  oxygen  from  the  ferric  compounds  and  reducing  them 
to  ferrous  compounds)  the  red  color  may  be  converted  to  gray,  or  even 
bluish  blade,  if  the  reduction  is  sufficient,  so  that  in  some  districts  the 
bricks,  on  account  of  lack  of  air  in  the  kilns  and  carbonaceous  matter 
in  the  clay,  do  not  burn  a  very  bright  red.  Moreover,  other  things 
being  equal,  the  higher  the  temperature  at  which  a  clay  is  burned,  the 
deeper  will  be  its  color. 

The  surface  coloration  of  a  burned  brick  may  often  be  different 
from  the  interior.  This  is  due  to  several  causes.  (1)  Soluble  salts 
may  accumulate  on  the  surface,  sometimes  causing  a  white  coating 


PHYSICAL   PROPERTIES   OF   CLAY  161 

because  they  have  been  drawn  out  by  the  evaporation  of  the  water 
during  the  drying  on  the  brick.1  (2)  The  deposition  of  foreign  sub- 
stances by  the  fire-gases  may  cause  a  colored  glaze.  This  is  especially 
seen  on  the  ends  of  arch-brick,  and  on  the  bag  walls  of  a  down-draft 
kiln,  where  the  particles  of  ash  carried  up  from  the  fires  stick  to  the 
surface  of  the  hot  brick  and  cause  a  fluxing  action.  (3)  If  the  clay 
contains  much  lime  carbonate,  and  there  is  much  sulphur  in  the  coal, 
the  latter  may  unite  with  the  lime,  forming  sulphate  of  lime,  and  thereby 
prevent  the  combination  of  the  lime  and  iron.  In  this  case  the  center 
of  the  brick,  not  being  thus  affected  by  the  gases,  may  show  a  buff  color, 
whereas  the  outside  has  another  tint. 

Loss  of  volatile  products  in  burning. — The  analyses  (see  table  on 
p.  160)  giving  the  composition  of  several  clays,  and  the  bricks  made 
from  them,  are  interesting  in  showing  the  loss  of  the  volatile  products 
in  burning. 

Color 

Color  of  unburned  clay. — An  unburned  clay  owes  its  color  commonly 
to  some  iron  compound  or  carbonaceous  matter,  more  rarely  manganese. 
A  clay  free  from  any  of  these  is  white. 

Carbonaceous  matter  will  color  a  clay  blue,  gray,  black,  or  even 
purplish,  depending  on  the  quantity  present,  3  per  cent  being  prob- 
ably sufficient  to  produce  a  deep  black;  clays  in  actual  use  having  some- 
times as  much  as  10  per  cent. 

Iron  oxide  colors  a  clay  yellow,  brown,  or  red,  depending  on  the 
form  of  oxide  present.  The  greenish  color  may  be  due  to  the  silicate 
of  iron,  and  in  some  clay  marls  of  the  Cretaceous  it  is  caused  by  the 
mineral  glauconite.  The  iron  coloration  is,  however,  often  concealed 
by  the  black  coloration  due  to  carbonaceous  matter,  and  it  is  sometimes 
more  or  less  difficult  to  make  even  an  approximate  estimate  of  the  iron 
content  in  a  clay  from  its  color.  Thus,  for  example,  two  clays  have 
been  noted  by  the  writer2  which  were  nearly  of  the  same  color  and 
had  respectively  3.12  and  12.40  per  cent  of  ferric  oxide. 

There  is  often  a  marked  difference  in  color  between  the  wet  and 
the  dry  clay,  in  fact  such  a  difference  at  times  as  to  make  one  doubt 
that  they  are  the  same  material.  The  dry  clay  is  usually  of  a  lighter 
tint. 

Color  of  burned  clay. — The  color  of  a  raw  or  unburned  clay  is  not 
always  an  indication  of  the  color  it  will  be  when  burned.  Red  clays 

1  See  "  Soluble  Salts  in  Clays,"  pp.  90  et  seq. 

2N.  J.  Geol.  Surv.,  Final  Report,  Vol.  VI,  p.  112,  1C04. 


162  CLAYS 

usually  burn  red;  deep-yellow  clays  may  burn  buff  or  red;  chocolate 
ones  commonly  burn  red  or  reddish  brown;  white  clays  burn  white 
or  yellowish  white;  and  gray  or  black  ones  may  burn  red,  buff,  or  white. 
Green  ones  usually  change  to  red  on  firing.  Calcareous  clays  are  often 
either  red,  yellow,  or  gray,  and  may  burn  red  at  first,  but  turn  cream, 
yellow,  or  buff  as  vitrification  is  approached,  and  show  a  greenish  yel- 
low at  viscosity. 

An  excess  of  alumina  seems  to  exert  a  bleaching  effect  similar  to 
that  of  lime. 

The  vitrification  of  ferruginous  clays  yields  browns,  greens,  and 
blacks,  due  to  the  formation  of  ferrous  silicates.1 

Seger  states  that  the  colors  which  a  burned  clay  may  show  depend 
on: 

1.  The  quantity  of  iron  oxide  contained  in  the  clay. 

2.  The  other  constituents  of  the  clay  accompanying  the  iron   (see 
Alumina  and  Lime). 

3.  The  composition  of  the  fire-gases  during  the  burning. 

4.  The  degree  of  vitrification. 

5.  The   temperature   at   which   the  clay   is  burned. 

The  same  author  has  attempted  to  classify  clays  according  to  their 
color-burning  qualities  as  follows:2 


Group. 

Character  of  clay. 

Color  after  burning. 

1 
2 
3 
4 

High  in  alumina  and  low  in  iron 
High  in  alumina  and  moderate  iron  contents 
Low  in  alumina  and  high  in  iron 
Low  in  alumina  and  high  in  iron  and  lime 

White,  or  nearly  so 
Pale  yellow  to  pale  buff 
Red 
Cream  or  yellow 

Slaking 

When  a  lump  of  raw  clay  or  shale  is  immersed  under  water'  it  falls 
to  pieces  or  slakes,  the  process  ceasing  only  when  the  clay  has  broken 
down  to  a  fine  powdery  mass.  The  time  required  for  this  varies  from 
a  few  minutes  in  the  case  of  soft  porous  clays  to  several  weeks  for 
tough  shales,  and  some  may  be  incompletely  disintegrated  even  after 
that. 

The  slaking  property  is  one  of  some  practical  importance,  as  easily 
slaking  clays  temper  more  readily,  or  if  the  material  is  to  be  washed, 
it  disintegrates  more  rapidly  in  the  log-washer. 

1  la.  Geol.  Surv.,  Vol.  XIV,  p.  59,  1904. 

2  Seger's  Collected  Writings,  Vol.  I,  p.  109. 


PHYSICAL  PROPERTIES  OF  CLAY  163 

Permeability 

An  interesting  series  of  experiments  has  been  made  by  W.  Spring,1 
who  finds  that  clay  when  under  pressure  and  confined  so  that  it  cannot 
expand  on  wetting  is  nearly  impervious  to  water;  under  such  condi- 
tions it  will  only  soak  up  enough  water  to  fill  the  pores.  The  percent- 
age of  water  thus  absorbed  may  range  from  as  low  as  3.37  per  cent  in 
glass-pot  clays  to  24.56  per  cent  in  some  loams.  Wet  clay  under  pres- 
sure will  part  with  its  water  even  though  the  mass  be  entirely  sur- 
rounded by  that  liquid. 


Adsorption 

By  this  term  is  meant  the  power  which  a  clay  has  of  removing  solid 
substances  from  solutions  with  which  it  is  in  contact. 

More  than  fifty  years  ago  T.  Way  2  noticed  that  clays,  and  soils 
with  a  clay  base,  possessed  extraordinary  powers  for  absorbing  water, 
but  that  in  addition  the  clay  substance  exhibited  greater  facility  for 
absorbing  the  bases  contained  in  certain  salts  which  were  dissolved, 
in  water.  This  action  was  also  selective,  certain  bases  and  substances 
being  held  so  that  they  could  not  be  washed  out  again. 

Bourry 3  states  that  kaolins  do  not  absorb  more  than  2  per  cent  of 
calcium  carbonate  from  a  solution,  while  plastic  clays  can  absorb  from 
10  to  20  per  cent  of  it.  More  recently  Dr.  Hirsch  4  has  made  a  number 
of  experiments  to  test  the  amount  of  dissolved  salts  which  a  clay  can 
absorb  when  stirred  up  in  a  solution.  He  found  that  clays  and  kaolins 
absorb  some  of  the  dissolved  salt,  because  after  settling  the  superna- 
tant liquid  had  a  lower  concentration  than  it  did  before;  but  sand  and 
burned  clay  do  not  show  this  power,  while  feldspar  and  marble  possess 
it  to  some  extent.  The  amount  of  salt  thus  absorbed  was  independent 
of  the  time,  and  the  removal  of  the  salt  ceased  with  the  settling  of  the 
clay.  It  is,  however,  dependent  on  the  kind  of  clay  and  kind  of  salt 
and  the  degree  of  concentration.  Thus  barium,  lead,  and  aluminum 
compounds  were  removed  in  considerable  quantities,  while  strontium, 
magnesium,  and  calcium  salts  were  absorbed  to  a  less  degree.  The 

1  Ann.  de  la  Soc.  geol.  de  Belg.,  XXVIII,  1901. 

2  Royal  Ag.  Soc.  Jour.,  XI,  1880.     Quoted  by  Cushman,  Trans.  Amer.  Cer. 
Soc.,  VI,  p.  7,   1904. 

3  Treatise  on  Ceramic  Industries,  p.  54,  1901. 

4  Thonindustrie-Zeitung,  No.  26,  1904. 


164  CLAYS 

acid  of  the  salt  seems  to  influence  the  result  appreciably.  Chlorides, 
nitrates,  and  acetates  are  absorbed  more  than  sulphates,  but  alkali 
salts,  except  the  carbonates,  are  not.  The  higher  the  concentration 
of  the  solution  the  greater  the  quantity  of  salt  absorbed,  although  in 
a  weak  solution  all  of  the  salt  may  be  carried  down.  The  conditions 
are  more  complicated  in  the  presence  of  several  salts;  thus  the  absorp- 
tion of  barium  chloride  is  decreased  by  the  presence  of  alkali  salts, 
acids  and  bases,  and  entirely  prevented  by  aluminum  chloride.  Sul- 
phates are  absorbed  in  the  presence  of  caustic  alkalies  and  acids,  while 
the  alkali  chlorides  seem  to  be  lacking  in  effect. 

Experiments  by  the  author  l  have  also  shown  that  some  tannins, 
as  gallo-tannic  acid,  are  absorbed  by  clay,  a  clear  filtrate  from  a  mix- 
ture of  gallo-tannic  acid  and  clay  giving  no  reaction  with  ferric  chloride. 

In  this  connection  it  is  of  interest  to  refer  to  the  observations  of 
Ivohler,2  who  finds  that  clays,  among  other  substances,  have  the  power 
-of  abstracting  metallic  oxides  from  solutions  which  are  filtered  through 
.them. 

E.  C.  Sullivan,3  in  experimenting  along  these  lines,  found  that 
when  a  solution  containing  100  cc.  of  water  with  252  grains  of  copper 
as  the  sulphate  was  shaken  up  with  powdered  orthoclase,  albite,  shale, 
•or  microcline,  it  was  found  that  there  was  a  remarkable  interchange 
of  bases  instead  of  absorption.  The  copper  entered  the  silicates,  and 
an  exact  molecular  equivalent  of  the  K2O,  Na2O,  CaO,  MgO,  or  MnO 
went  into  solution.  The  feldspar  proved  much  more  efficient  than 
kaolin,  and  removed  from  60  to  100  per  cent  of  the  copper  from  the 
liquid. 

1  Trans.  Amer.  Ceram.  Soc.,  VI,  p.  44,  1906. 

2  Adsorptionsprozesse  als  Faktoren  der  Lagerstattenbildung  und  Lithogenesis 
Zeitschr.  fur  prakt.  Geologie,  Feb.  1903,  p.  49. 

3  The  Chemistry  of  Ore  Deposition,  Jour.  Amer.  Chem.  Soc.,  XX VII,  p.  976 
and  Economic  Geology,  I,  p.  67,  1905. 


CHAPTER  IV 
KINDS  OF  CLAYS 

IN  this  chapter  it  is  proposed  to  give  briefly  the  characters  of  the 
clays  employed  for  different  purposes,  beginning  with  the  highest  grades. 

Kaolins 

This  term  as  commonly  used,  and  it  seems  to  the  author  the  cor- 
rect way  to  use  it,  refers  to  those  white-burning  clays  of  residual  char- 
acter,1 which  are  composed  mostly  of  silica,  alumina,  and  chemically 
combined  water,  and  have  a  very  low  percentage  of  fluxing  impurities, 
especially  iron.  In  this  country  they  have  been  formed  chiefly  by 
the  weathering  of  pegmatite  veins,  and  in  rarer  instances  from  feld- 
spathic  quartzites,2  limestone,3  and  talcose  schists.4  There  are  some 
other  occurrences,  as  those  of  Edwards  County,  Texas,  and  the  indi- 
anaite  of  Indiana,5  whose  exact  origin  does  not  seem  satisfactorily 
proven. 

In  Europe  they  have  been  formed  by  the  alteration  (in  most  cases 
probably  by  weathering)  of  other  rock  types,  especially  granite  and 
quartz-porphyry. 

The  mode  of  origin  of  kaolin,  and  changes  accompanying  same, 
have  been  discussed  on  another  page  (p.  8),  and  it  need  simply  be 
repeated  here  that  kaolins  formed  by  weathering  will  grade  downward 
into  the  parent  rock,  while  the  depth  of  those  caused  by  fluoric  action 
will  depend  on  the  depth  of  the  parent  rock  and  the  extent  of  the  path 
through  it  of  the  kaolinizing  vapors. 

1  The  white-burning  sedimentary  clays  found  in  the  coastal  plain  area  of  the 
Southern  Atlantic  States  are  at  times  termed  kaolins,  but  it  would  seem  wiser,  per- 
haps, to  term  these  plastic  kaolins  to  distinguish  them  from  the  residual  ones. 

2  H.  Ries,  Private  publication  of  the  Kaolin  Co.,  Cornwall,  Conn. 

3  Wheeler,  Mo.  Geol.  Surv.,  XI,  p.  162,  1896. 

4  Hopkins,  Ann.  Kept.  Pa.  State  College,  1898-99. 
BBlatchley,  Ind.  Dept.  Geol.  and  Nat.  Res.,  XXIX,  p.  55,  1904. 

165 


166 


CLAYS 


Most  kaolins  as  mined  are  rather  siliceous,  but  in  their  washed  con- 
dition approach  closely  to  the  composition  of  kaolinite,  from  which  it 
has  been  sometimes  argued  that  kaolins  are  composed  chiefly  of  kaolinite 


MAP  SHOWING 

DISTRIBUTION  OF 

KAOLIN  AND  BALL-CLAY  DEPOSITS 

IN 

EASTERN    UNITED  STATES 


LEGEND 
•  Kaolin  Deposits 
*Ball  Clay  Deposits 


FIG.  36. — Map  showing  kaolin  and  ball-clay  deposits  of  United  States,  east  of  the 
Mississippi  River.     (After  H.  Ries,  U.  S.  Geol.  Surv.  Prof.  Pap.  11,  p.  284,  1903.) 

and  quartz.     The  author  himself  held  this  view  for  some  time,  but 
now  feels  that  it  is  not  safe  to  make  such  a  broad  statement. 

The  incorrectness  of  this  theory  becomes  apparent  if  we  examine 
any  series  of  kaolin  analyses,  from  which  it  can  be  seen  that  the  alumina- 
silica  ratio  is  often  higher  than  that  required  for  kaolinite,  and  this 


KINDS  OF  CLAYS  167 

seems  best  accounted  for  on  the  supposition  that  some  of-  the  other 
hydrous  aluminum  silicates,  such  as  pholerite  or  halloysite,  are  present. 

Again,  a  washed  kaolin  might  have  as  much  as  20  per  cent  white 
mica,  and  yet  on  analysis  show  a  composition  approaching  rather  closely 
to  that  of  kaolinite. 

All  of  these  minerals — kaolinite,  pholerite,  halloysite,  and  muscovite — 
are  decomposed  by  treatment  with  hot  sulphuric  acid,  and  therefore 
reported  in  the  rational  analysis  as  clay  substance.  This  is  unfortunate, 
because  mica  is  not  refractory  and  should  not  therefore  be  grouped 
with  the  other  three. 

There  is  also  the  possibility  that  in  some  highly  aluminous  kaolins 
some  aluminum  hydroxide,  such  as  bauxite  orgibbsite,  might  be  present. 

Chemical  composition. — The  analyses  shown  on  page  168  of  both 
native  and  foreign  kaolins,  will  give  some  idea  of  their  composition. 
All  of  these  are  washed  samples  with  the  exception  of  No.  I.  A  com- 
parison of  analyses  I  and  II  will  therefore  show  the  beneficial  effects 
of  washing. 

It  will  be  noticed  that  all  of  these  analyses  show  a  small  percentage 
of  alkalies,  due  probably  to  the  presence  of  some  undecomposed  feldspar 
or  muscovite. 

Physical  tests. — When  tested  physically  they  all  show  a  low  air- 
shrinkage,  low  tensile  strength,  are  white-burning,  and  usually  highly 
refractory.  The  following  tests  bring  out  these  points  well: 

1.  Kaolin  from  Harris  Clay  Company,  Webster,  N.  C. — Works  up 
with  42  per  cent  of  water  to  a  lean  mass.     Air-shrinkage,  6  per  cent; 
fire-shrinkage  at  cone  9,  4  per  cent;  average  tensile  strength,  22  pounds 
per  square  inch;  fuses  about  cone  33.1 

2.  Kaolin  from  Glen  Allen,  Mo. — Requires  23.2  per  cent  of  water 
to  work  it  up  to  a  lean  paste  whose  air-shrinkage  is  4  per  cent  and  fire- 
shrinkage,  at  2500°  F.,  8.4  per  cent;  average  tensile  strength,  12  pounds 
per  square  inch;    incipient  fusion,  2200°  F.;    vitrification  at  2500°  F.2 

3.  Kaolin,  Oak  Level,  Henry  County,  Va. — Water  required,  48.4 
per  cent;    plasticity  and  tensile  strength,  low;    air-shrinkage,  1.6  per 
cent;  fire-shrinkage,  cone  9,  8  per  cent,  with  absorption  36.08  per  cent; 
fusion-point  above  cone,  27. 

Distribution. — The  known  workable  deposits  of  kaolin  found  in 
the  United  States  are  all  located  east  of  the  Mississippi  River,  with  the 
exception  of  those  found  in  Missouri,  Utah,  and  Texas.  The  last- 
named  two  are  not  worked.  The  distribution  of  those  east  of  the 

1  N.  C.  Geol.  Surv.,  Bull.  13,  p.  59,  1897. 

2  Mo.  Geol.  Surv.,  XI,  p.  578. 


168 


CLAYS 


Mississippi  River  is  shown  in  Fig.  36,  and  the  Missouri  deposits  in 
Fig.  56.  Reference  is  made  to  their  occurrence  undei  the  state  descrip- 
tions in  Chapters  VI  and  VII. 

ANALYSES  OF  KAOLINS 


I. 

II. 

III. 

IV. 

V. 

VI. 

Silica  (SiO2)  

62.40 

45.78 

46.28 

73.80 

46.50 

72.30 

Alumina  (A12O3)  

26.51 

36.46 

36.25 

17.30 

37.40 

18.94 

Ferric  oxide  (Fe  Oo) 

1  14 

28 

1  644 

35 

80 

40 

Ferrous  oxide  (FeO) 

1  08 

Lime  (CaO) 

57 

50 

192 

tr. 

68 

Magnesia  (MgO)  . 

01 

.04 

.321 

1  18 

39 

Potash  (K2O)                        .      1 

f  1  69 

2  49 

\  , 

Soda  (Na2O)  .  .           J 

.98 

.25 

1     .85 

.20 

jl.l 

.42 

Titanium  oxide  (TiO2)  

Water  (H2O)  

8.80 

13.40 

13.535 

4.69 

12.49 

7.04 

Moisture  

.25 

2.05 

Total  

100.66 

99.84 

100.763 

100.01 

98.29 

100.17 

VII. 

VIII. 

IX. 

X. 

XI. 

Silica  (SiO  ) 

45  44 

46  38 

48  26 

46  87 

47  71 

Alumina  (Al  O3) 

40  30 

39  76 

37  64 

38  00 

36  78 

Ferric  oxide  (Fe  O3) 

54 

79 

46 

89 

Ferrous  oxide  (FeO) 

Lime  (CaO) 

tr. 

.44 

06 

tr 

Magnesia  (MgO)  .               

tr. 

05 

tr. 

.35 

Potash  (K2O) 

f   tr. 

1.80 

Soda  (Na2O)  

1     .38 

.20 

j  1.56 

1.22 

2.58 

Titanium  oxide  (TiO2)  

.28 

Water  (H2O)  

13  9 

10.26 

12.02 

12.70 

13.03 

Moisture  

Total. 

100  56 

99.96 

100.00 

100.03 

100.10 

I.  Webster,  N.  C.     Crude  kaolin.     N.  C.  Geol.  Surv.,  Bull.  13,  p.  62,  1897. 

II.  Webster,   N.   C.     Washed  kaolin.     Ibid. 

III.  Brandywine  Summit,  Pa.     Hopkins,  Pa.  State  Coll.,  App.  Kept.,  1898-99,  p.  36. 

IV.  Upper  Mill,  Pa.     T.  C.  Hopkins,  Ann.  Kept.,  Pa.  State  Coll.,  1899-1900,  p.  11. 
V.  West  Cornwall,  Conn.     H.  Ries,  Anal. 

VI.  Glen  Allen,  Mo.     Mo.  Geol.  Surv.,  XI,  p.  562,  1896. 

VII.  Leaky,  Edwards  County,  Texas.     O.  H.  Palm,  Anal. 

VIII.  Oak  Level,  Henry  County,  Va.     Analyzed  by  Va.  Geol.  Surv. 

IX.  Cornwall,  Eng.  . 1 

X.  Zettlitz,  Bohemia [  U.  S.  Geol.  Surv.,  Prof.  Pap.  11,  p.  39,  1903. 

XI.  Co ussac- Bonne val,  France J 

Kaolins  after  washing  are  used  in  the  manufacture  of  white  ware, 
porcelain,  floor  and  wall  tiles,  paper  manufacture,  and  as  an  ingre- 
dient of  slips  and  glazes. 

Ball-clay 

This  includes  those  white-burning  plastic  clays  of  sedimentary 
character  which  are  extensively  used  as  a  necessary  .ingredient  of  white- 
ware  mixtures  in  order  to  give  the  body  sufficient  plasticity  and  bond- 


KINDS  OF  CLAYS 


169 


ing  power.  They  must  therefore  contain  little  or  no  iron  oxide,  and 
possess  good  plasticity  and  tensile  strength.  Refractoriness  is  desir- 
able, but  those  imported  vitrify  at  cone  8,  while  the  native  ones  require 
a  much  higher  heat  for  vitrification.  Some  ball-clays  as  those  of  Florida 
require  washing  before  shipment  to  market. 

Chemical  composition. — The  following  table  gives  the  composition 
of  several  American  ball-clays,  as  well  as  that  of  an  English  ball-clay: 

ANALYSES  OF  BALL-CLAYS 


I. 

II. 

III. 

IV. 

V. 

Silica  (SiO2)     . 

46  11 

45  57 

56  40 

45  97 

48  99 

Alumina  (A12O3) 

39  55 

38  87 

30  00 

36  35 

32  11 

Ferric  oxide  (Fe2O3).  . 

35 

1  14 

1  08 

Ferrous  oxide  (FeO).  . 

2  34 

Lime  (CaO)  

tr. 

40 

1   14 

43 

Magnesia  (MgO)  

13 

11 

tr. 

1  09 

22 

Potash  (K2O)  

16 

3  261 

f  3  31 

Soda  (Na2O)  

00 

2  01  J 

1.84 

Titanium  oxide  (TiO2)  

i  26 

1  30 

Sulphur  trioxide  (SO3)  

07 

Water  (H,O)  

13  78  \ 

/  7  93 

12  36 

9  63 

Moisture  

( 

14.10 

Total  

101  19 

101  25 

100  00 

99  83 

97  03 

I.  Edgar,  Fla.     U.  S.  Geol.  Surv.,  Prof.  Pap.  11,  p.  39. 

II.  Woodbridge,  N.  J.     N.  J.  Geol.  Surv.,  Fin.  Kept.  VI,  p.  443. 

III.  Mayfield,  Ky.     U.  S.  Geol.  Surv.,  Prof.  Pap.  11,  p.  39. 

IV.  Regina,  Mo.     Mo.  Geol.  Surv.,  XI,  p.  566,  1896. 
V.  "Poole"  clay,  Wareham,  Eng. 

Physical  characters. — The  physical  properties  of  some  of  the  well- 
known  ball-clays  used  in  this  country  are  as  follows: 

Edgar,  Fla. — Very  plastic;  average  tensile  strength,  150  pounds 
per  square  inch;  total  shrinkage  at  cone  9,  15  per  cent. 

Woodbridge,  N.  J. — Water  required,  33  per  cent;  plasticity,  fair; 
air-shrinkage,  3.4  per  cent;  average  tensile  strength,  33  pounds  per 
square  inch.  At  cone  10,  fire-shrinkage  16.6  per  cent  and  absorption 
0.22  per  cent;  fusion-point,  cone  34. 

Distribution. — The  number  of  known  localities  in  the  United  States 
at  which  ball-clays  occur  is  small,  and  are  shown  in  Figs.  36  and  55.  They 
are  obtained  from  the  Tertiary  (Florida,  Kentucky,  Tennessee)  and 
Cretaceous  (New  Jersey)  formations,  and  in  residual  deposits  derived 
from  Palaeozoic  limestones  (Missouri). 


170  CLAYS 

Fire-clays 

The  term  fire-clay,  properly  speaking,  refers  to  those  clays  capable 
of  withstanding  a  high  degreee  of  heat,  but  it  is  unfortunately  most 
loosely  used  by  American  clay-workers,  and  many  plastic  materials 
which  have  absolutely  no  claim  to  refractoriness  are  included  under 
this  head.  It  is  to  be  greatly  regretted  that  no  standard  of  refractori- 
ness has  been  adopted  in  the  United  States,  nor  for  that  matter  in 
Europe,  although  the  use  of  the  term  is  probably  less  abused  there 
than  here.  In  the  author's  opinion  no  clay  should  be  classed  as  a 
fire-clay  unless  its  fusion-point  is  higher  than  that  of  cone  27. 

Aside  from  refractoriness,  which  is  the  most  important  property  of 
a  fire-clay  and  the  one  possessed  by  all  true  ones,  they  vary  widely, 
showing  great  differences  in  plasticity,  density,  shrinkage,  tensile  strength, 
and  color.  Since  the  resistance  of  a  fire-clay  to  heat  is  governed  pri- 
marily by  ire  chemical  composition  and  secondarily  by  its  texture,  it 
may  be  well  to  consider  first  the  former  property. 

Chemical  composition — Fire-clays  contain  practically  all  the  sub- 
stances usually  determined  by  the  ultimate  analysis  (p.  58),  but  in  every 
good  fire-clay  the  total  percentage  of  certain  fluxing  impurities,  such  as 
ferric  oxide,  lime,  magnesia,  and  alkalies,  is  small.  This  is  necessarily 
the  case,  since,  if  the  fluxing  impurities  were  present  in  large  quan- 
tities, the  clay  would  fuse  at  comparatively  low  temperatures  and 
could  not  be  classed  as  refractory. 

Effect  of  silica. — It  is  found,  however,  that  clays  running  low  in 
fluxes  but  high  in  silica  may  also  show  poor  refractoriness.  If  we 
compare  two  fire-clays  of  low-flux  contents,  but  high  silica  in  one  case 
and  low  silica  in  the  other,  it  is  found  that,  other  things  being  equal, 
the  high-silica  clay  is  less  refractory  than  the  other.  This  indicates 
that  a  high  percentage  of  silica,  as  well  as  a  high  percentage  of  the 
fluxes  mentioned  above,  diminishes  the  refractoriness  of  the  clay.  We 
might,  therefore,  term  the  iron  oxide,  lime,  magnesia,  and  alkalies  low- 
temperature  fluxes  and  the  silica  a  high-temperature  flux. 

In  any  fire-clay  some  of  the  silica  is  combined  chemically  with 
the  alumina  and  water,  forming  a  hydrous  aluminum  silicate  which 
for  convenience  of  discussion  we  assume  is  kaolinite,1  while  the  balance 
is  probably  there  in  the  form  of  quartz.2  If  kaolinite  alone  is  heated, 

1  It  probably  is  in  most  fire-clays. 

2  There  cannot  be  many  silicate  minerals,  such  as  feldspar,  mica,  etc.,  in  a  fire- 
clay, otherwise  the  percentage  of  alkalies,  magnesia,  lime,  and  iron  oxide  would 
be  higher  than  it  usually  is,  so  that  the  balance  of  the  silica  must  be  quartz. 


PLATE  VII 


Impure 
clay 


Coal 


Fire-clay 


pIG  i — Section  showing  fire-clay  underlying  coal-seam.  The  upper  clay  above 
coal  is  of  impure  character.  (Photo  loaned  by  Robinson  Clay-product  Com- 
pany.) 


FIG.  2. — Fire-clay  underlying  Lower  Mercer  limestone,  Union  Furnace,  O. 

(Photo  by  B.  S.  Fisher.)  171 


KINDS  OF  CLAYS  173 

its  refractoriness  is  found  to  be  high,  for  its  fusion-point  is  the  same 
as  cone  36  of  the  Seger  series,  and  the  refractoriness  of  quartz  or  silica 
alone  is  nearly  as  high,  but  if  these  two  minerals  are  mixed  together 
in  varying  proportions,  then  the  fusion-point  of  the  mixtures  will  in 
every  case  be  lower  than  that  of  either  silica  or  kaolinite  alone. 

This  fact  was  pointed  out  some  years  ago  by  Seger,1  who  made 
up  a  series  of  mixtures  of  alumina  and  silica,  and  kaolin  and  silica.  In 
the  former  series  of  mixtures  the  quantity  of  alumina  in  each  case  was 
the  same,  but  the  amount  of  silica  was  increased.  Starting  with  1  part 
of  alumina  to  1  of  silica  by  volume  (91.5  of  alumina  to  8.5  of  silica  by 
weight2),  a  mixture,  the  fusion-point  of  which  was  the  same  as  that 
of  cone  37,  he  found  that  the  refractoriness  decreased  until  a  mixture 
of  1  part  alumina  to  17  parts  of  silica  (10  alumina  to  90  silica  by  weight) 
was  reached.  The  fusing-point  of  this  mixture  was  cone  29.  A  fur- 
ther increase  in  the  amount  of  silica  caused  the  refractoriness  to  rise 
steadily.  This  shows  that  silica  added  to  alumina  in  certain  propor- 
tions acts  as  a  flux  at  high  temperatures. 

If  now  silica  is  mixed  with  kaolinite  in  the  same  manner,  a  similar 
lowering  of  the  refractoriness  of  the  body  takes  place  down  to  a  cer- 
tain point  beyond  which  the  fusion-point  again  rises.  These  experi- 
ments of  Seger  are  shown  graphically  in  Fig.  33,  in  which  the  horizontal 
lines  represent  the  different  cone  numbers  from  26  to  38  inclusive.  The 
divisions  on  the  lower  line  represent  percentages  of  alumina  or  kaolin 
measured  above  the  line,  100  per  cent  being  at  the  left  end,  and  per- 
centages of  silica  measured  below  the  line,  100  per  cent  being  at  the 
right  end.  The  solid  curve  represents  the  mixtures  of  silica  and  alumina, 
while  the  dotted  curve  represents  mixtures  of  kaolin  and  silica.  An 
inspection  of  these  curves  shows  quite  clearly  how  an  increase  in  the 
percentage  of  silica  up  to  a  certain  point  causes  a  dropping  of  the  fusion- 
point,  but  that  a  further  increase  in  the  silica  contents  raises  it  again, 
although  not  quite  as  high  as  it  originally  was. 

It  will  be  seen  from  a  comparison  of  these  two  curves  that  the  kao- 
linite-silica  mixtures  have  lower  refractoriness  than  the  pure  silica-alu- 
mina mixtures.  This  effect  of  silica  has  not  always  been  understood 
by  fire-brick  manufacturers,  many  believing  that  sand  added  to  the  refrac- 
toriness of  a  clay  in  burning.  While  this  is  indeed  true  in  the  case  of 

1  bc-^or,  Gesammelte  Schriften,  p.  434,  1896.     Amer.  Ceram.  Soc.,  Translation, 
I,  p.  545. 

2  What  is  meant  here  is  parts  by  volume  which  would  not  be  the  same  as  parts 
by  weight,  because  the  two  substances  have  different  specific  weights,  hence  1  alu- 
mina to  1  silica  per  volume  would  be  91.5  per  cent  alumina  to  8.5  silica  by  weight. 


174 


CLAYS 


brick-clays,  it  is  to  be  remembered  that  common  brick  is  burned  at 
at  a  much  lower  temperature  than  that  at  which  alumina  and  silica 
unite. 

Recent  tests  made  on  a  series  of  fire-clays  from  New  Jersey 1  agreed 
with  Seger's  results  in  a  general  way  but  not  exactly,  the  plotted  fusion- 
points  forming  a  curve  on  which  corresponding  points  were  somewhat 
lower  than  those  on  Seger's. 

In  order  to  test  his  experiments  a  series  of  mixtures  of  a  white- 
burning  clay  (having  practically  the  composition  of  kaolinite)  and 
finely  ground  quartz  were  made  up  and  their  fusion-points  tested  in. 
the  Deville  furnace.  These  results  were  plotted  in  a  curve  (Fig.  37)  > 


Cone  No.  30 
35 
34 
33 
32 
31 
30 
29 
28 
27 
26 
25 
21 
Kaolin  100 

1 

»*^1 

IX 

Kaolin  a 

id  Silica 

X 

X 

X 

X 

\ 

V    XII 

XVIII 

9 

\ 

I 

\ 

\ 

X 

XV 

I 

^^ 

XIV  1 

f            8 

0            8 

)            7 

)            6 

9             5 

0             4 

0             3 

0            2 

)             10 

10            20            30            10            50            GO            70           80             90          10( 

FIG.  37. — Diagram  showing  effects  of  silica  on  fusibility  of  kaolin. 
(After  Ries,  N.  J.  Geol.  Surv.,  Fin.  Kept.  VI,  p.  313,  1904.) 

which  in  its  general  form  agrees  with  that  of  Seger,  but  shows  lower 
cones  of  fusion  for  corresponding  mixtures.  The  results  obtained  with 
New  Jersey  clays  seem  to  agree  more  closely  with  this  curve  than  they 
did  with  Seger's.  (Fig.  33.) 

Applying  the  facts  obtained  from  these  experiments  to  a  study 
of  fire-clays  it  would  seem  that,  other  things  being  equal,  those  fire- 
clays will  be  the  most  refractory  which  contain  the  lowest  percentage 
of  fluxing  impurities,  such  as  iron,  lime,  magnesia,  and  alkalies,  and 
the  smallest  quantity  of  sand  or  silica  not  in  combination  with  the 
alumina  of  kaolinite,  or  some  other  hydrous  aluminum  silicate. 

1  N.  J.  Geol.  Surv.,  Fin.  Kept.,  VI,  p.  314,  1904. 


KINDS   OF  CLAYS 


175 


The  following  analyses  and  fusion-tests  made  on  a  series  of  New 
Jersey  clays  are  of  interest  as  showing  the  relation  of  the  composition 
to  the  fusing-point. 

ANALYSES  OF  SOME  NEW  JERSEY  FIRE-CLAYS 


1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 

10. 

11. 

12. 

13. 

g 
3   . 

M 

ox 

1 

1 

fusion. 

O 

Jo 

w^1 

0 

'S'M 

«9i 

.so 

^o 

J 

55 

« 

•8 

i5 

'£# 

Is 

S>S 

as 

Is 

| 

3 

I 

3 

1 

a 

a 

£ 

-3 
02 

1 

6 

I. 

50.60 

34.  3i 

0.78 

tr. 

tr. 

tr. 

1.62 

12.90 

87.20 

10.65 

0.78 

34  + 

II. 

51.56 

33.13 

0.78 

0.12 

1.91 

12.50 

83.94 

13.25 

0.90 

34  + 

III. 

68.67 

21.46 

0.78 

1.35 

1.34 

6.40 

52.82 

43.71 

2.13 

27 

with 

IV. 

67.26 

23.36 

1.63 

0.25 

.... 

0.65 

Al?03 

6.94 

57.47 

40.09 

2.53 

27 

with 

V. 

45.76 

39.05 

tr. 

0.95 

0.04 

A1203 

14.46 

98.93 

0.24 

0.9£ 

34  + 

VT. 

69.78 

19.86 

0.62 

1.24 

1.96 

6.54 

49.50 

46.68 

i.se 

30 

with 

VII. 

40.64 

41.  K 

3.27 

0.65 

Al,08 

14.74 

96.57 

3.92 

29 

I.  No.  1  fire-clay,  M.  D.  Valentine  &  Bro.  (Loc.  14),  Woodbridge. 

II.  No.  1  fire-clay,  Anness  &  Potter  (Loc.  6),  Woodbridge. 

III.  Top  sandy  clay,  Anness  &  Potter  (Loc.  6),  Woodbridge. 

IV.  Fire-mortar  clay,  Maurer  &  Son  (Loc.  24),  Woodbridge., 
V.  Ware  clay,  W.  H.  Cutter  (Loc.  29),  Woodbridge. 

VI.  No.  1  sandy  clay,  McHose  Bros.  (Loc.  45),  Florida  Grove. 

VII.  No.  1  blue  fire-clay,  J.  R.  Grossman  (Loc.  65),  Burt  Creek. 

*  Exclusive  of  titanium.      This  probably  stands  intermediate  between  silica  and  the  other 
fluxes  in  its  fluxing  power,  but  nearest  to  silica. 

"In  this  table  the  second  to  ninth  columns  inclusive  represent  the 
determinations  made  in  the  ultimate  analysis.  A  partial  analysis  only 
of  some  of  the  samples  was  available,  and  in  these  cases  the  difference 
between  the  sum  of  the  substances  determined  and  100  was  taken  as 
representing  the  sum  of  the  lime,  magnesia,  and  alkalies.  The  clay  base 
given  in  the  tenth  column  was  obtained  by  considering  the  alumina 
to  be  contained  in  kaolinite,  figuring  the  amount  of  silica  necessary  to 
unite  with  it,  and  adding  the  combined  water  to  it;  the  total  of  the  three 
then  represents  the  clay  base.1  The  difference  between  the  silica  neces- 
sary to  combine  with  the  alumina  and  form  the  clay  base  and  the  total 
silica  was  considered  as  representing  the  free  silica.  The  twelfth  column 


1  The  amount  of  water  present  as  an  ingredient  of  limonite  is  so  small  in  these 
cases  that  it  can  be  neglected. 


176  CLAYS 

represents  the  sum  of  the  iron  oxide,  lime,  magnesia,  and  alkalies.  The 
last  column  gives  the  cone  of  fusion. 

"Examining  the  percentages  given  we  see  that  in  the  first  analysis 
the  percentage  of  clay  base  is  87.20  per  cent  and  silica  10.65  per  cent, 
while  the  total  fluxes  are  0.78  per  cent.  Comparing  these  percentages 
with  the  curve  (Fig.  37),  we  see  that  a  mixture  of  90  per  cent  kaolinite 
and  10  per  cent  silica  (IX),  which  is  close  to  the  composition  of  clay 
No.  I  of  the  table,  melted  at  cone  34,  so  that  the  0.78  per  cent  fluxes 
probably  exert  little  influence. 

"  Again,  in  the  third  analysis,  the  percentage  of  clay  base  or  kaolinite 
is  52.82  per  cent  and  that  of  the  silica  43.71  per  cent;  from  the  curve 
in  Fig.  37  such  a  mixture  would  fuse  at  approximately  cone  29.  But 
we  have  here  in  addition  to  the  silica  2.13  per  cent  total  fluxes,  so  that 
we  should  expect  the  clay  to  fuse  at  a  still  lower  cone.  By  actual  test 
the  fusion-point  was  found  to  be  cone  27,  so  that  evidently  both  the  free 
silica  and  fluxes  present  force  down  the  fusing-point  and  the  facts  cor- 
respond to  the  theory. 

"No.  IV  of  the  table  of  analyses  behaves  similarly  to  No.  Ill,  and 
No.  V  has  a  high  fusing-point,  on  account  of  its  high  percentage  of  clay 
substance  and  low  amount  of  fluxes. 

"In  the  case  of  No.  VI  we  find  that,  leaving  the  fluxes  out  of  considera- 
tion, a  mixture  of  kaolinite  and  silica  in  the  proportions  shown  in  this 
clay  should  fuse  at  about  cone  30,  and  the  amount  of  lime,  magnesia, 
alkalies,  and  titanium  oxide  given  in  the  analysis  should  lower  the  fusion- 
point  to  at  least  cone  29  or  even  28.  As  it  is,  the  fusion-point  as  deter- 
mined is  cone  30,  and  there  is  an  apparent  disagreement  between  theory 
and  the  facts.  This  is  probably  explainable  by  the  fact  that  the  clay 
is  a  very  sandy  one,  and,  therefore,  since  much  of  the  silica  is  in  the 
form  of  coarse  grains,  it  is  not  able  to  enter  into  active  chemical  union 
with  the  clay  base.  In  any  event  this  sample  illustrates  the  fact  that  the 
fusion-point  of  a  clay  cannot  be  determined  solely  from  a  chemical 
analysis.  No.  VII  owes  its  low  refractoriness  to  a  high  content  of  total 
fluxes  and  not  to  high  silica  contents.  This  clay  has  a  silica-alumina 
ratio  of  0.97,  and  it  would  therefore  appear  as  if  some  other  hydrous 
aluminum  silicate  than  kaolinite  were  present  (see  Pholerite,  p.  50). 
Were  it  not  for  nearly  4  per  cent  of  fluxes,  its  refractoriness  would  be 
quite  high.  These  few  samples,  will,  however,  serve  to  show  the  practica 
application  of  the  facts  mentioned  above." 

Effect  of  titanium. — It  will  be  noticed  that  the  percentage  of  titanium 
oxide  has  been  determined  separately  in  several  of  the  above  analyses, 
and  from  the  quantity  present  it  is  believed  to  exert  some  influence.  As 


KINDS   OF  CLAYS  177 

has  been  mentioned  under  Titanium  (p.  84),  the  presence  of  2  per  cent 
of  titanium  seems  to  lower  the  refractoriness  a  whole  cone  number,  while 
0.5  per  cent  lowered  it  half  a  cone  when  it  was  mixed  with  kaolin  alone. 

Physical  properties. — As  mentioned  above,  the  term  fire-clay  does 
not  signify  the  presence  of  any  other  character  than  refractoriness,  and 
fire-clays  may  therefore  vary  widely  in  their  plasticity,  shrinkage,  texture, 
color,  tensile  strength,  and  other  physical  properties,  all  of  which  affect 
the  behavior  of  the  clay  during  the  process  of  manufacture,  but  none 
of  which  can  be  used  as  a  sure  guide  in  determining  its  probable  refractori- 
ness. Color  may  be  an  aid  under  certain  conditions,  since  pure  white 
clays  and  light  yellowish  clays  are  often  at  least  semi-refractory  and 
sometimes  highly  refractory.  Some  fire-clays  are  tinged  a  deep  yellow 
or  yellowish  red,  as  though  they  contained  considerable  iron  oxide,  and 
yet  they  have  excellent  heat-resisting  power.  If  the  clay  is  black  or 
bluish  black,  there  is  no  means  of  telling  from  mere  inspection  what 
its  heat-resisting  qualities  are,  for  under  these  conditions  both  a  clay 
with  very  little  iron  oxide  and  one  with  much  might  outwardly  appear 
the  same. 

Plasticity  has  little  or  no  direct  relation  to  refractoriness,  although 
Seger  has  pointed  out  that  of  two  clays  of  unequal  refractoriness  the 
one  of  lower  fire-resisting  qualities  may  withstand  the  action  of  molten 
materials  better  if  it  is  of  high  plasticity,  as  this  makes  it  burn  to  a  dense 
body  at  a  comparatively  low  temperature.  The  result  of  this  is  that 
the  pores  are  closed  and  the  clay  resists  the  corrosive  action  of  a  fused 
mass  better  than  the  more  refractory  clay,  which  does  not  burn  dense 
at  as  low  a  temperature  as  the  first  one,  and  which,  therefore,  permits 
a  molten  mass  to  enter  the  pore-spaces  between  its  grains. 

Fire-clays  are  of  variable  tensile  strength.  Some  of  the  highest 
grades  show  low  tensile  strength  and  often  require  a  more  plastic  material 
to  raise  it,  such  an  addition  being  sometimes  necessarily  done  at  a  slight 
sacrifice  of  refractoriness. 

Analyses  of  fire-clays. — The  analyses  shown  on  page  178  give  the 
composition  of  a  number  of  fire-clays  from  various  localities  in  the 
United  States,  and  for  additional  ones  reference  should  be  made  to  the 
State  descriptions. 

Occurrence  and  distribution. — Fire-clays  may  be  of  either  residual 
or  sedimentary  origin,  and  of  the  two  the  latter  are  by  far  the  most 
important  commercially.  This  class  is  further  subdivisible  into  plastic 
fire-clays  and  flint-clays.  The  former  are  plastic  when  wet,  the  latter 
are  hard  and  flint-like,  with  a  smooth,  shell-like  fracture  and  dense 
texture.  They  develop  but  little  plasticity,  even  when  ground  fine, 


178 


CLAYS 

ANALYSES  OF  FIRE-CLAYS 


I. 

II. 

III. 

IV. 

V. 

VI. 

Silica  (SiO2)  

74.25 
17.25 
1.19 

63.00 
23.57 
.46 

1  87 

52.52 
31.84 
.67 

59.92 
27.56 
1.03 

62.89 
21.49 

51  .  92 
31.64 

Alumina  (A12O3)  

Ferric  oxide  (Fe2O3)  

Ferrous  oxide  (FeO)  

1.81 
.38 
.56 

2.52 

1.13 
.03 
.44 

.40 

Lime  (CaO)  

.40 
tr. 

.52 

.44 

.89 
(2.401 
I     -29J 

.50 
.19 

.59 

tr. 
tr. 

.67 

Potash  (K  O)                              \ 

Soda  (Na2O)  J 

Sulphur  trioxide  (SO3)  

Titanic  acid  (TiO  )  . 

1.10 
6.45 

1.68 
11.68 

"9".  70' 

1.82 

7.58 
1   16 

1.16 
13.49 

Water  (H  O) 

6.30 

Moisture  

Total 

99.91 

100.47 

99.67 

98.88 

100.21 

100.21 

VII. 

VIII. 

IX. 

X. 

XI. 

XII. 

Silica  (SiO2)  

51.56 
33.13 

.78 

46.56 
37.47 
tr. 

59.36 
23.26 
3.06 

61.44 
26.18 
.30 
36 

73.00 
15.79 
.63 

50  .  35 
33.64 
.75 

Alumina  (A12O3)  

Ferric  oxide  (Fe  O3) 

Ferrous  oxide  (FeO)  

Lime  (CaO) 

tr. 
tr. 
tr. 
tr. 

.112 
tr. 

.281 

.28] 

.65 
.42 

.63 
.35 

.12 

1.29 
1.53 
.10 
.16 

tr. 
.49 
.09 

.80 
11.75 
2.13 

Magnesia  (MsrO)  • 

Potash  (K  O) 

/ 

Soda  (Na  O) 

1     .02 

Sulphur  trioxide  (SO3)  

Titanic  acid  (TiO2)  

1.91 

1.01 
/  10.  20 
I  2.74 

1.39 
9.07 

.77 

.43 
5.76 

Water  (H2O).           \ 

12.50 

13.03 

Moisture  / 

Total  

99.88 

97.732 

101.68 

99.65 

98.69 

100.00 

I.  Bibbville,  Ala.     Ala.  Geol.  Surv.,  Bull.  6,  p.  152,  1900. 
II.  Mecca,  Parke  County,  Ind.     Ind.  Dept.  Geol.  and  Nat.  Res.,  29th  Ann.  Kept.,  p.  507,  1905. 
III.  Mineral  Point,  O.  (Flint-clay).     Mo.  Geol.  Surv.,  XI,  p.  591,  1896. 
IV.  Saline  ville,  O.  (Flint-clay).     Ohio  Geol.  Surv.,  VII,  p.  221,  1893. 
V.  Lower  Kittanning  clay,  New  Brighton,  Pa.,  2d  Pa.  Geol.  Surv.,  MM,  p.  262. 
VI.  Bolivar  flint  fire-clay,  Salina,  Pa.     Ibid.,  p.  259. 
VII.  Woodbridge,  N.  J.     No.  1  fire-clay,  N.  J.  Geol.  Surv.,  VI,  p.  441,  1904. 
VIII.  Boone  Furnace,  Ky.     Coal  measures,  U.  S.  Geol.  Surv.,  Prof.  Pap.  11,  p.  119. 
IX.  St.  Louis,  Mo.     Mo.  Geol.  Surv.,  XI,  p.  571,  1896. 
X.  Piedmont,  W.  Va.     Mount  Savage  clay,  W.  Va.  Geol.  Surv.,  III. 
XI.  Athens,  Tex.     O.  H.  Palm,  analyst. 
XII.  Golden,  Colo.     U.  S.  Geol.  Surv..  Mon.  XXVII,  p.  390 

but  are  usually  highly  refractory.  Flint-clays  are  found  at  a  number  of 
points  in  the  Carboniferous  of  Pennsylvania,  Ohio,  Maryland,  Kentucky,, 
and  West  Virginia,  where  they  occur  often  underlying  coal-seams  and 
in  the  same  bed  with  the  plastic  clay,  the  two  showing  no  regularity  of 
arrangement,  and  often  differing  but  little  if  at  all  in  chemical  composi- 
tion. Their  peculiar  character  has  been  a  puzzling  problem  to  geologists,, 
but  it  seems  probable  that  they  may  have  been  formed  by  a  solution  and 
reprecipitation  of  the  clay  by  percolating  water  subsequent  to  its  forma- 


KINDS  OF  CLAYS  179 

tion.  A  second  type  of  flint-clay  is  that  found  occupying  basins  in. 
Palaeozoic  limestones  in  Missouri  (which  see). 

In  many  States  1  fire-clays  are  often  found  underlying  coal-beds,  and 
on  this  account  it  has  been  suggested  that  their  alkalies  and  other  fluxing; 
impurities  have  been  abstracted  by  the  roots  of  plants  which  grew  in. 
the  swamps  in  which  these  clays  were  deposited,  while  the  decay  of 
these  plants  later  gave  rise  to  the  coal-bed  overlying  the  clay.  This 
theory  seems  rather  improbable,  as  in  some  States,  such  as  Michigan 
and  Alabama,  the  clays  and  shales  underlying  the  coals  always  contain 
sufficient  impurities  to  render  them  non-refractory.  Furthermore,  tha 
extensive  beds  of  refractory  clay,  found  in  the  Tertiary-Cretaceous: 
formations  of  the  Atlantic  and  Gulf  coastal  plains,  are  very  rarely- 
associated  with  coal-beds. 

We  must,  therefore,  assume  that  these  clays  were  either  derived  from 
rocks  running  low  in  fusible  impurities,  or  else  that  these  were  removed 
by  solution  during  the  transportation  and  deposition  of  the  clay  particles.. 

In  the  United  States  fire-clays  are  widely  distributed,  both  geologically 
and  geographically.  The  most  important  occurrences  are  in  the  Car- 
boniferous of  Ohio,  Pennsylvania,  Kentucky,  Indiana,  Illinois,  Maryland, 
West  Virginia,  and  Missouri.  Many  other  deposits  are,  however,  found  in 
the  Cretaceous  of  New  Jersey,  Maryland,  Georgia,  South  Carolina,  Ala- 
bama, Texas,  Iowa,  Colorado,  South  Dakota,  etc.,  and  in  the  Tertiary 
of  New  Jersey,  Georgia,  South  Carolina,  Alabama,  Texas,  Arkansas,  and 
California. 

In  Pennsylvania,  Maryland,  Alabama,  and  North  Carolina  some  pre- 
Devonian  ones  occur,  but  they  are  of  limited  extent. 

Uses. — The  main  use  of  fire-clays  is  for  the  manufacture  of  the  various- 
shapes  of  fire-brick,  but  in  addition  they  are  used  wholly  or  in  part 
in  the  manufacture  of  gas-  and  zinc-retorts,  locomotive  and  furnace 
linings,  crucibles,  floor-tiles,  terra-cotta,  conduits,  pressed  and  paving 
bricks,  etc. 

Glass-pot  clays  form  a  special  grade  used  in  the  manufacture  of  glass 
pots  and  blocks  for  glass-tank  furnaces.  These  require  a  clay  which 
is  not  only  refractory  but  burns  dense  at  a  moderately  low  temperature, 
so  that  it  will  resist  the  fluxing  action  of  the  molten  glass. 

It  must  possess  good  bonding  power  and  burn  without  warping. 
Great  care  is  necessary  in  the  selection  of  the  clay  and  the  manufacture 
of  the  pot.2 

1  Ohio,  Pennsylvania,  Kentucky,  Indiana,  and  West  Virginia. 

2  Ries,  U.  S.  Geol.  Surv.,  Min.  Res.,  1901. 


180  CLAYS 

In  testing  a  glass-pot  clay  physical  tests  are  of  more  value  than 
chemical  analyses.  Glass-pot  clay  is  obtained  from  both  Pennsyl- 
vania and  Missouri,  but  much  is  still  imported  from  the  Gross-Almerode 
district  of  Germany. 

Stoneware-clays 

Physical  properties. — Stoneware  is  usually  made  from  a  refractory 
or  semi-refractory  clay,  but  at  some  small  potteries  a  much  lower  grade 
•of  material  is  used.  The  proper  physical  qualities  are  of  paramount 
importance.  Stoneware-clay  should  have  sufficient  plasticity  and 
toughness  to  permit  its  being  turned  on  a  potter's  wheel,  this  depending 
partly  on  the  amount  of  clay  substance  present  and  on  the  fineness  of 
the  sand.  A  size  of  grain  of  from  0.002  to  0.01  of  an  inch  for  the  non- 
plastic  grains  in  stoneware  clays  has  proved  to  be  most  suitable.  Coarse 
sand  renders  the  clay  so  absorbent  that  it  will  not  hold  its  shape  in 
.turning.1 

A  tensile  strength  of  125  Ibs.  per  square  inch  or  over  is  desirable,  and 
the  clay  should  also  show  low  fire-shrinkage,  good  vitrifying  qualities, 
;and  yet  sufficient  refractoriness  to  make  the  ware  hold  its  shape  in 
burning.  Concretionary  minerals,  such  as  iron  or  lime,  which  are  liable 
to  cause  blisters,  should  be  avoided.  Most  stoneware  is  now  made  from 
a  mixture  of  clays,  so  as  to  produce  a  body  of  the  proper  qualities,  both 
before  and  after  burning. 

Chemical  composition. — Orton  2  gives  the  following  average  of  ten 
separate  analyses  of  stoneware-clays  in  use  in  Ohio  potteries: 

Clay  base 56.65 

Sandy  matter -  •  •  37 . 45 

Fluxing  matter 4 . 44 

Moisture 1 . 57 

100.14 
Total  silica 65 .09 

A  high  silica  content  was  formerly  considered  essential  in  order 
to  produce  a  successful  salt-glaze,  but  this  feature  is  of  little  importance 
now  as  other  kinds  of  glazes  are  almost  exclusively  used. 

The  following  analyses  give  the  composition  of  stoneware  clays  from 
a  number  of  different  localities. 

1  la.  Geol.  Surv.,  XIV,  p.  233,  1904. 

2  Ohio  Geol.  Surv.,  VII,  p.  95,  1893. 


KINDS  OF  CLAYS 


181 


ANALYSES  OF  STONEWARE  CLAYS 


I. 

II. 

III. 

IV. 

V. 

VI. 

VII. 

VIII. 

Silica  (SiO  ) 

67  10 

71  94 

67  84 

57  20 

64  26 

68  3 

60  34 

69  2& 

Alumina  (A12O3).  . 

19  37 

17  60 

21  83 

24  82 

22  95 

20  1 

20  55 

18  97 

Ferric  oxide  (Fe2O3).  .  . 
Ferrous  oxide  (FeO). 

2.88 

2.35 

1.57 

3.25 
1  42 

1.28 

1.0 

tr 

3.53 
49 

1.57 
55 

Lime  (CaO)  .     . 

tr. 

62 

28 

73 

45 

tr 

38 

12 

Magnesia  (MgO)  

.725 

.56 

24 

.13 

37 

2  4 

1  12 

36 

Potash  (K20)  
Soda  (Na2O)  

.672 

1.50 

2.24 

.93 

1.96 

tr. 
.6 

2.89 
.73 

2.27 
33 

Titanic  acid  (TiO2).  .  .  . 

1.2 

.92 

1  5 

Water  (H2O)  

6.08 

5.27 

5.9 

8.25 

6.74 

6.6 

6.42 

5  46 

Moisture  

1.71 

1.01 

.8 

2.10 

2.05 

2.35 

Phosphorous  acid  (P<>Oe) 

55 

Total  

98.537 

100.85 

100.70 

97.41 

100.06 

100  .  20 

100.27 

100.37 

I.  Thirteen  miles  from  Fayette  C.  H.,  Fayette  County,  Ala.     Ala.  Geol.  Surv.,  Bull.  6,  p.  176, 

1900. 
II.  Calhoun,  Henry  County,  Mo.     Mo.  Geol.  Surv.,  XI,  p.  564,  1896. 

III.  Woodbridge,  Sussex  County,  N.  J.     N.  J.  Clay  Kept.,  1878,  p.  99. 

IV.  Lincolntoii,  N.  C.     N.  C.  Geol.  Surv.,  Bull.  13,  p.  78,  1897. 

V.  Akron,  Summit  County.,  O.     Ohio  Geol.  Surv.,  VII,  p.  94,  1893. 
VI.  Elmendorf,  Bexar  County,  Tex.     O.  H.  Palm,  anal. 

VII.  Bridgeport,  Harrison  County,  W.  Va.     W.  Va.  Geol.  Surv.,  Ill,  p.  162,  1906. 
VIII.  Huntingburg,  Ind.     Ind.  Dept.  Geol.  and  Nat.  Res.,  29th  Ann.  Kept.,  p.  508,  1904. 

Physical  tests. — The  following  data  will  serve  to  illustrate  the  physical 
characters  of  some  stoneware  clays: 

Calhoun,  Henry  County,  Mo. — A  very  plastic,  buff-burning  clay  re- 
quiring 16.5  per  cent  water;  average  tensile  strength,  150  Ibs.  per  sq., 
in.;  air-shrinkage,  5.5  per  cent;  fire-shrinkage,  2.2  per  cent;  incipient 
fusion,  2100°  F.;  vitrification,  2300°  F.;  viscosity,  2500°  F.1 

Northport,  Long  Island,  N.  Y. — A  yellow  sandy  clay  requiring  25 
per  cent  water,  and  having  fair  plasticity;  average  tensile  strength,  25 
pounds  per  square  inch;  air-shrinkage,  5.5  per  cent.;  fire-shrinkage,  6.5 
per  cent;  nearly  vitrified  at  2300°  F;  viscous  at  cone  27.  This  is  mixed 
with  a  more  plastic  clay  for  use.2 

South  Amboy,  N.  J. — No.  2  stoneware  clay.  Water  required,  37 
per  cent;  average  tensile  strength,  109  Ibs.  per  sq.  in.;  air-shrinkage,. 
7  per  cent;  fire-shrinkage  at  cone  10,  9  per  cent  and  absorption  .24  per 
cent;  viscous  at  cone  30.3 

Athens,  Henderson  County,  Tex.— Water  required,  26.4  per  cent; 
average  tensile  strength,  143  Ibs.  per  sq.  in.;  air-shrinkage,  6.9  per  cent- 
At  cone  9,  fire-shrinkage,  6  per  cent;  color,  buff;  absorption,  7.45  per 
cent;  viscous  at  cone  30.4 

1  Mo.  Geol.  Surv.,  XI,  p.  575,  1896. 
J  N.  Y.  State  Museum,  Bull.  35,  p.  821,  1900. 
1  N.  J.  Geol.  Surv.,  Fin.  Kept.,  VI,  p.  459,  1904. 
4  Unpublished  notes. 


182  CLAYS 

It  will  be  noticed  that  no  examples  are  given  from  Ohio  or  Indiana, 
'both  important  producers  of  stoneware  clays,  the  reason  for  this  being 
that  no  tests  have  been  published. 

Stoneware  clays  are  used  not  only  for  the  manufacture  of  all  grades 
of  stoneware,  but  also  for  yellow  ware,  art  ware,  earthenware,  and  more 
recently  even  for  terra-cotta. 

Terra-cotta  Clays 

Terra-cotta  is  made  from  many  different  kinds  of  clay,  but  most 
manufacturers  of  this  material  are  now  using  semi-fire  clays,  or  a  mixture 
of  these  with  a  more  impure  clay  or  shale,  since  these  give  the  best 
results  at  the  temperatures  (cone  6-8)  usually  attained  in  their  kilns. 
Some  are  used  because  of  their  dense-burning  character  and  bonding 
power,  others  because  of  a  low  shrinkage  and  freedom  from  warping, 
while  absence  of  soluble  salts  is  an  important  as  well  as  desirable  property 
In  all. 

Buff-burning  clays  are  commonly  chosen,  partly  because  they  burn 
to  a  hard  body  at  the  desired  temperature,  and  there  is  little  danger  of 
overburning.  The  color  of  the  body  is  of  no  great  importance,  since 
the  final  color  is  applied  superficially.  Very  few  terra-cotta  manu- 
facturers at  the  present  day  employ  a  low-grade  clay. 

The  soluble  salts  are  undesirable,  because  in  drying  they  may  come 
out  through  the  color-slip,  but  they  can  be  rendered  insoluble,  if  necessary, 
by  treating  the  clay  with  barium  chloride  or  carbonate. 

To  give  a  tabulated  statement  of  the  properties  of  clays  used  for 
terra-cotta  manufacture  would  involve  listing  a  very  large  number. 
It  may  be  of  interest,  however,  to  give  the  properties  of  a  terra-cotta 
mixture  used  at  a  large  Eastern  factory,  the  tests  being  made  on  a  soft 
green  body,  as  tempered  at  the  works.  Its  physical  properties  were 
as  follows: l 

Air-shrinkage,  4J  per  cent;  tensile  strength,  97.5  Ibs.  per  sq.  in.  Its 
.behavior  in  burning  was  as  follows: 

Cone  01.  Cone  5.                            Cone  10. 

Fire-shrinkage 1.5%  4.8%                            5% 

Hardness not  steel-hard  nearly  steel-hard 

Absorption very  absorbent  slightly  absorbent  nearly  impervious 

Color pale  buff  gray  buff                     gray  buff 

In  making  terra-cotta  the  clay  is  not  carried  to  the  temperature 
last  given,  as  there  would  be  danger  of  its  warping,  but  it  is  usually 

1  N.  J.  Geol.  Surv.,  Final  Kept.,  VI,  p.  270,  1904. 


KINDS   OF  CLAYS 


183 


fired  between  cones  6  and  8,  at  which  point  this  danger  is  greatly,  if 
not  entirely,  diminished. 

The  table  on  page  184  giving  the  physical  character  of  some  of  the 
New  Jersey  clays  used  for  terra-cotta  manufacture  shows  what  a  variety 
of  materials  are  employed.1 

Clays  suitable  for  terra-cotta  manufacture  are  widely  distributed, 
but  those  mostly  used  in  this  country  are  the  Cretaceous  clays  of  New 
Jersey  and  the  Carboniferous  clays  of  Pennsylvania,  Indiana,  and 
Missouri. 

Sewer-pipe  Clays 

Since  sewer-pipes  have  to  be  vitrified  in  burning/they  require  a  clay 
high  in  fluxes,  and  the  clays  employed  are  similar  to  those  needed  for 
paving-brick  manufacture,  so  that  the  two  products  are  sometimes 
made  at  the  same  factory  from  the  same  clay.  Ordinarily,  some  fire- 
clay is  mixed  in  with  the  verifiable  material,  to  hold  its  shape  better 
in  burning.  A  high  iron  percentage  is  said  to  aid  the  formation  of  the 
salt-glaze  with  which  the  pipes  are  covered,  but  a  high  percentage  of 
soluble  salts  is  objectionable. 

The  following  are  analyses  of  sewer-pipe  clays  from  various  localities: 

ANALYSES  OF  SEWER-PIPE  CLAYS 


I. 

II. 

III. 

IV. 

V. 

Silica  (SiO  )                

57.10 

55.60 

63.00 

59.96 

57  52 

21.29 

24.34 

23.57 

15.76 

21  76 

Kprrif*  oxidf*  (Fe  O  ^ 

7.31 

6.11 

1.87 

7  72 

3  41 

Ferrous  oxide  (FeO) 

.46 

3  70 

JLime  (CaO)         

.29 

.43 

.44 

.60 

.60 

1.53 

.77 

.89 

.93 

.88 

Potash  (K2O)   

3.44 

3.00 

2.40 

3.66 

3  57 

Soda  (Na2O)  

.61 

.09 

.29 

.03 

Titanium  oxide  (TiO  ) 

1.10 

83 

Water  (H2O)  

6.00 

6.75 

6.45 

7.70 

7.27 

1.30 

2.65 

.86 

Sulphur  trioxide  (SO3)                    

73 

Phosphorus  pentoxide  (P2O5)  

14 

Total  

98.87 

99.74 

99  88 

98  06 

99.57 

I.  Shale,  Canton,  O-     Ohio  Geol.  Surv.,  VII,  p.  133,  1893. 
II.  Shale  and  fire-clay  mixture.     Ibid. 
•III.  Underclay,  Mecca,  Parker  County,  Ind.     Ind.  Dept.  Geol.  and    Nat.  Res.,  29th  Ann.  Kept., 

p.  114,  1904. 

IV.  Laclede  mine,  St.  Louis,  Mo.     Mo.  Geol.  Surv.,  XI,  p.  570,  1896. 

V.   Kittanning  clay.      JStna   mine,   New  Cumberland,    W.   Va.     W.    Va.   Geol.   Surv..   Ill,  p. 
219,  1906. 


1  N.  J.  Geol.  Surv.,  Final  Kept.,  VI,  p.  270,  1904. 


184 


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KINDS  OF  CLAYS 


185 


The  sewer-pipe  clays  in  the  Eastern  and  Central  States  are  obtained 
chiefly  from  the  Carboniferous  formations,  and  to  a  small  extent  from 
the  Devonian  ones.  The  Cretaceous  and  Tertiary  beds  of  the  coastal 
plain  States  are  not  as  a  rule  adapted  to  sewer-pipe  manufacture,  but 
in  the  Rocky  Mountain  region  and  Black  Hills  area  some  of  the  Creta- 
ceous shales  have  good  vitrifying  qualities.  Pleistocene  clays  are  used 
only  to  mix  in  with  the  other  materials. 

Brick-clays 

Common  brick. — The  clays  or  shales  used  for  common  brick  are 
usually  of  a  low  grade,  and  in  most  cases  red-burning.  The  main  requis- 
ites are  that  they  shall  mold  easily  and  burn  hard  at  as  low  a  temperature 
as  possible,  with  a  minimum  loss  from  cracking  and  warping.  Since 
many  common  clays  or  shales  when  used  alone  show  a  higher  air-  and 
fire-shrinkage  than  is  desirable,  it  is  customary  to  decrease  this  by  mixing 
some  sand  with  the  clay  or  by  mixing  a  loamy  or  sandy  clay  with  a  more 
plastic  one. 

Common-brick  clays  vary  widely  in  their  composition,  but  most  of 
them  contain  a  rather  high  percentage  of  fluxing  impurities. 

While  the  chemical  composition  is  of  importance  in  affecting  the 
color-burning  qualities  and  fusibility  of  the  mass,  the  physical  characters 
are  even  more  important,  since  they  affect  not  only  the  color  in  burning 
but  often  exert  an  influence  on  the  process  of  molding  to  be  chosen. 

The  following  analyses  will  serve  to  represent  their  range  in  com- 
position : 

ANALYSES  OF  BRICK-CLAYS 


I.* 

II. 

III. 

IV. 

V. 

VI. 

VII. 

VIII. 

IX. 

Silica  (SiO2).  .  .  . 
Alumina  (A12O3). 
Ferric  oxide 
(Fe,O,) 

66.67 
18.27 

3.11 
1.18 
1.09 
2.92 
1.30 

.85 
4.03 

71.50 
13.86 

4.78 
.56 
.11 
2.29 
.81 

1.44 
4.61 

42.28 
8.26 

3.84 
13.05 
6.01 
2.51 
.49 

.05 
122.07 

68.62 
14.92 

4.16 
1.48 
1.09 
1.50 
1.86 

52.30 
18.85 

6.55 
3.36 
4.49 
4.65 
1.35 

56.50 
19.31 

5.89 
l.OOo 
1.85a 

5.98 

88.71 
4.88 

2.00 
.30 
.97 
tr. 
tr. 

18.62 
3.23 

1.26 
41.  3C 
.42 

56.81 
20.62 

6.13 
.65 

.58 
4.47 

Lime  (CaO)  
Magnesia  (MgO). 
Potash  (K2O)  .  .  . 
Soda  (Na2O)  
Titanic  acid 
(TiO2)  

.90 

2.28 

tr. 

2.42 
32.50 

8.60 

Water  (H2O).... 
Carbon  dioxide 
(CO2)  

3.55 
.64 

5.30 
3.04 

9.47& 

Marsanese 
dioxide(MnO2) 
Moisture  

2.78 

1.64 

Total  

99.42 

99.96 

98.56 

100.60 

99.89 

100.0C 

100.04 

99.75 

99.50 

a.  Determined  as  carbonate.     6.  Includes  organic  matter. 
*For  references  see  foot  of  table,  page  186. 


186  CLAYS 

PHYSICAL  PROPERTIES  OF  SOME  or  THE  PRECEDING 


I. 

II. 

III. 

VI. 

VII. 

Per  ce 
Plasti 
Air-sh 
Avera 

nt  water  required 

22 
Good 
6 
108 

20.9 
Good 
6.4 
89.6 

0 
17.40 

1.6 
15.08 

5 

7.1 

Red 

19.8 
High 
6.5 
316 

.4 
23.23 

slightly 
swelled 
22.63 

2.7 
16.35 

Cream 

32 
Good 
6 
105 

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Red 

20.9 
Low 
6.6 

117 

city                    .... 

rinkage  .               

ge  tensile  strength,  Ibs.  per  sq.  in  .  . 

Cone 
010 

Fire-shrinkage  

Absorption  

4.3 

7.88 

8.6 
.1 

Red 

0 
11.77 

0 
13.27 

Red 

Cone 
05 

Fire-shrinkage 

Absorption. 

Cone 
1 

Fire-shrinkage  

Absorption.  .  .          . 

Color 

when  burned.  ...             .    . 

I.   Pleistocene  clay,  Little  Ferry,  N.  J.     N.  J.  Geol.  Surv.,  VI,  220,  1904. 
II.  Pleistocene  clay,  Richmond,  Va.     Va.  Geol.  Surv.,  Bull.  II,  p.  130,  1906. 

III.  Calcareous  Pleistocene  clay,  Whitewater,  Wis.     Wis.  Geol.  and  Nat.  Hist.  Surv.,  Bull.,  1906. 

IV.  Loess,  Gut  one  Centre,  la.     la.  Geol.  Surv.,  XIV,  p.  541,  1904. 

V.   Salina  shale,  Warners,  N.  Y.     N.  Y.  State  Mus.,  Bull.  35,  p.  830,  1900. 
VI.  Carboniferous  shale,  Grand  Rapids,  Mich.     Mich.  Geol.  Sun-.,  VIII,  Pt.  I,  p.  41,  1899. 
VII.  Pleistocene  brick-loam,  Texarkana,  Tex.     O.  H.  Palm,  anal. 
VIII.   Seguin,  Guadalupe  County,  Tex.     O.  H.  Palm,  anal. 
IX.  Residual  clay,  Greensboro,  N.  C.     N.  C.  Geol.  Surv.,  Bull.  13,  p.  114,  1897. 

Some  pretty  poor  clays  are  at  times  used  for  common-brick  manu- 
facture, but  this  is  due  to  the  fact  that  common  brick  will  not  always 
bear  the  cost  of  transportation,  and  it  is  sometimes  necessary  to  use 
the  best  material  that  can  be  obtained  locally,  even  though  it  be  not 
thoroughly  satisfactory. 

Common-brick  clays  are  widely  distributed,  both  geologically  and 
geographically. 

Two  varieties  of  brick-clay,  of  common  occurrence  west  of  the  Missis- 
sippi River,  may  be  mentioned  here. 

Adobe. — This  is  a  calcareous  silty  clay,  common  throughout  the 
Southwestern  States  and  much  used  for  making  sun-dried  or  adobe  brick. 

Analyses  of  some  adobe  soils,  showing  their  calcareous  character, 
are  given  on  page  187. 

Loess. — This  name  has  been  applied  to  extensive  Pleistocene  deposits, 
which  are  not  unlike  adobe,  but  regarding  whose  origin  there  has  been 
much  dispute,  some  claiming  them  to  be  of  subaqueous  origin,  while 
others  consider  them  to  be  seolian  formations.  The  loess  is  a  very 
common  deposit  throughout  the  Mississippi  Valley,  and  much  used  for 
brickmaking.  Analyses  by  Russell l  are  given  in  the  second  table  on 
page  187. 

1  Geol.  Mag.,  VI,  pp.  289  and  342,  1889- 


KINDS   OF  CLAYS 

ANALYSES  OF  ADOBE  SOILS 


187 


I. 

11. 

III. 

Silica  (SiO8)  

58  19 

19  24 

66  69 

Alumina  (A12O3)  

11  19 

3  26 

14  16 

Ferric  oxide  (Fe2O3).  . 

2  77 

1  OQ 

4  ^8 

Lime  (CaO).  . 

12  16 

38  94 

2  4Q 

Magnesia  (MgO).  ..    . 

80 

2  75 

i    28 

Potash  (K2O)  

tr 

tr 

1   21 

Soda  (Na2O)  

18 

tr 

67 

Titanium  oxide  (TiO2)  

1.05 

Water  (H2O)  

2  00 

1  67 

4  84 

Carbon  dioxide  (CO2).  .             ... 

8  00 

29  57 

77 

Phosphorus  pentoxide  (P2O6)  

23 

29 

Sulphur  trioxide  (SO3)  

53 

41 

Chlorine  (Cl)   

11 

34 

Organic  matter  

2  96 

2  00 

Total  

96.34 

100  35 

99  53 

I.   Laredo,  Tex.     O.  H.  Palm,  anal. 

II.   Salt  Lake  City,  Utah.     L.  G.  Elkins,  anal.     U.  S.  Geol.  Surv.,  Bull.  228,  p.  367,  1904. 
III.  Santa  Fd,  N.  Mex.     Ibid.,  p.  368. 


ANALYSES  OF  LOESS 


I. 

II. 

III. 

IV. 

Silica  (SiO0)                                

72  68 

64  61 

74  46 

60  69 

Alumina  (Al2Oo).            

12  03 

10  64 

12  26 

7  95 

Ferric  oxide  (Fe2O3)  

3  53 

2  61 

3  25 

2  61 

Ferrous  oxide  (FeO)  

.96 

51 

12 

67 

Lime  (CaO)                                         v 

1  59 

5  41 

1  69 

8  96 

Magnesia  (MgO) 

1  11 

3  69 

1  12 

4  56 

Potash  (K  O) 

2  13 

2  06 

1  83 

1  08 

•Soda  (Na  O) 

1  68 

1  35 

1  43 

1  17 

Titanic  oxide  (TiO2)                              .... 

72 

40 

14 

52 

Phosphorus  pentoxide  (P2O5)   

23 

06 

09 

13 

Manganese  oxide  (MnO)   .       

06 

05 

02 

12 

Carbon  dioxide  (CO2)  

39 

6  31 

49 

9  63 

Sulphur  trioxide  (SO3)  

51 

11 

06 

12 

Carbon  (C)      .               

09 

13 

12 

19 

Water  (HO)  

2  50o 

2  05« 

2  70a 

1  14a 

Total            

100.21 

99.99 

99.78 

99  54 

a.  Contains  H  of  organic  matter  dried  at  100°  C. 

Pressed  brick. — Pressed  brick  call  for  a  higher  grade  of  clay.  The 
kinds  now  in  use  fall  mostly  into  one  of  three  groups,  namely,  1,  red -burn- 
ing clays;  2,  white-burning  clays;  3,  buff-burning  clays,  usually  semi- 
refractory.  The  composition  of  a  sample  of  these  three  types  is  given 
in  the  table  at  top  of  page  188. 

The  physical  requirements  of  a  pressed-brick  clay  are  (1)  uniformity 


188 


CLAYS 

ANALYSES  OF  PRESSED-BRICK  CLAYS 


I. 

II. 

III. 

Silica  (SiO2) 

68  28 

63  11 

65  78 

Alumina  (A12O3). 

18  83 

93  30 

14  79 

Ferric  oxide  (Fe0O3)  

2  60 

2  23 

8  03 

Lime  (CaO)  

70 

73 

54 

Magnesia  (MgO)  

13 

97 

1  42 

Potash  (K2O)  \ 

/      93 

2  82 

Soda  (\a  O)                                                                             / 

2.29 

1       4Q 

97 

Titanium  oxide  (TiO2) 

07 

i     •  ^^ 

1  00- 

Water  (H  O) 

G  47 

7  81 

4  98 

Moisture 

Silp'iur  trioxida  (3O3) 

.  , 

I.  A  cliy  used  for  white  brick,  Grover,  N.  C.     N.  C.  Geol.  Surv.,  Bull.  13,  p.  81,  1897. 
II.   Hocking  Valley,  O.,  clay.     L.  E.  Barringer,  anal.     Supplied  by  A.  V.  Bleininger. 
III.  Shale  from  Cayuga,  Vermillion  County,  Ind.     Ind.  Dept.  Geol.  and  Nat.  Res.,  29th  Ann. 
Kept.,  p.  503,  1904. 

of  color  in  burning,  (2)  freedom  from  warping  or  splitting,  (3)  absence 
of  soluble  salts,  and  (4)  sufficient  hardness  and  low  absorption  when 
burned  at  a  moderate  temperature.  The  air-shrinkage  and  fire-shrinkage, 
as  well  as  tensile  strength,  vary  within  the  same  limits  as  common  bricks. 

Red-burning  clays  were  formerly  much  used,  but  in  recent  years 
other  colors  have  found  greater  favor,  and  the  demand  for  the  former 
has  greatly  fallen  off.  Buff-burning,  semi-refractory  or  refractory 
clays  are,  therefore,  much  employed  now,  partly  on  account  of  their 
color  and  partly  because  coloring  materials  can  be  effectively  added  to 
them,  for  since  the  range  of  natural  colors  that  can  be  produced  in  burning 
is  limited,  artificial  coloring  agents  are  sometimes  used.  Manganese  is 
the  one  most  employed. 

The  clays  must  necessarily  burn  hard  at  a  moderate  temperature, 
and  in  the  case  of  red-burning  clays  the  temperature  reached  may  range 

PHYSICAL  PROPERTIES  OF  SOME  NEW  JERSEY  CLAYS  USED  FOR  FRONT  BRICK.  1 


Formation. 

Water 
required, 
per  cent. 

Air- 
shrinkage, 
per  cent. 

Average 
tensile 
strength, 
Ibs.  per 
sq.  in. 

Cone 
of  firing. 

Fire- 
shrink- 
age, 
percent. 

Absorption, 
per  cent. 

Color. 

Raritan 

32  00 

5  0 

65 

fCone  1 

\  Cone  5 

5  0 

11    68  }• 

Buff 

Cohansey  
Cohansey  

23.17 
37.50 

7.5 
5.5 

282 
196 

[Cone  8 
[Cone  1 
\  Cone  5 
[Cone  8 
Cone  8 

6.6 

2.8 
4.5 
6.5 
9.1 

11.34J 

8.09] 
3.08  J- 
0.84J 
4.01 

Buff 
Buff 

1  N.  J.  Geol.  Surv.,  Fin.  Kept.,  VI,  p.  222,  1904. 


KINDS  OF  CLAYS  189 

from  the  fusing-point  of  cone  06  to  2,  while  for  buff-burning  clays  it  is 
commonly  necessary  to  go  to  cone  7  or  8  to  get  a  steel-hard  brick,  unless 
calcareous  materials  are  employed,  and  these  are  not  burned  above 
cone  3,  or  even  cone  1. 

In  the  table  at  bottom  of  page  188  are  given  the  physical  characters 
of  some  New  Jersey  pressed-brick  clays.  The  properties  of  a  shale  quar- 
ried at  North  Bluff,  Kansas  City,  Mo.,1  are:  water  required,  22.3;  plas- 
ticity, high;  air-shrinkage,  6.9  per  cent;  fire-shrinkage,  4.8  per  cent; 
average  tensile  strength,  198  Ibs.  per  sq.  in.;  incipient  fusion,  1600°  F.; 
vitrification,  1750°  F.;  viscosity,  1900°  F.;  color  when  burned,  red. 

Flashing.2 — Many  bricks  used  for  fronts  are  often  darkened  on  the 
€dges  by  special  treatment  in  firing,  caused  chiefly  by  setting  them 
so  that  the  surfaces  to  be  flashed  are  exposed  to  reducing  conditions, 
-either  at  the  end  of  the  firing  or  during  the  entire  period  of  burning. 
This  color  is  superficial  and  may  range  from  a  light  gold  to  a  rich,  reddish 
brown.  The  principle  of  the  operation  depends  on  the  formation  of 
ferrous  silicate  and  ferrous  oxide  and  their  subsequent  partial  oxidation 
to  the  red  or  ferric  form.  This  oxidation  probably  takes  place  during 
cooling,  for  if  the  kiln  be  closed  so  as  to  shut  off  the  supply  of  oxygen, 
the  bricks  are  found  to  be  a  light  grayish  tint. 

The  degree  of  flashing  is  affected  (1)  by  the  composition  and  physical 
condition  of  the  clay,  (2)  the  temperature  of  burning,  (3)  the  degree  of 
reduction,  and  (4)  the  rate  of  cooling  and  the  amount  of  air  then  admitted 
to  the  kiln. 

1.  The  percentage  of  iron  oxide  should  not  be  large  enough  to  make 
the  brick  burn  red,  but  to  produce  buff  coloration,  and  the  clay  should 
have  sufficient  fluxes  to  reduce  the  point  of  vitrification  to  within  reason- 
able limits,  thus  facilitating  the  flashing.  Clays  high  in  silica  are  appar- 
ently better  adapted  to  flashing  than  those  low  in  silica  and  high  in 
alumina.  The  condition  in  which  the  iron  is  present  in  the  clay  probably 
exerts  some  influence,  that  is,  whether  it  is  there  as  ferric  oxide,  ferrous 
silicate,  concretionary  iron,  ferrous  sulphide,  or  perhaps  ferrous  carbonate. 
Bleininger's  experiments  showed  that  of  three  clays  which  were  used 
for  flashing,  all  contained  considerable  quantities  of  iron  soluble  in  acid. 
Some  Eastern  manufacturers  are  obliged  to  add  magnetite  ores  to  their 
clays,  which  are  low  in  combined  iron,  and  No.  2  fire-clays,  which  contain 
more  iron  than  the  finer  grades,  seem  to  give  the  best  results.  As  to 
the  effect  of  the  physical  condition  of  the  clay,  finer  grinding  seems  to 
give  more  uniform  flashing  effects,  and  the  reason  that  stiff-mud  bricks 

1  Mo.  Geol.  Surv.,   XI. 

2  A.  V.  Bleininger,  Notes  on  Flashing.     Trans.  Amer.  Ceramic  Soc.,  II,  p.  74. 


190  CLAYS 

flash  better  than  dry-press  ones  is  claimed  by  some  to  be  due  to  vitrifica- 
tion taking  place  more  easily  in  the  former. 

The  following  analysis  gives  the  composition  of  a  No.  2  fire-clay  from 
Ohio  used  for  flashed  brick: 

ANALYSIS  OF  AN  OHIO  No.  2  FIRE-CLAY 

Silica  (SiO2) 67 . 14 

Alumina  (A12O3) 19 . 74 

Ferric  oxide  (Fe2O3) 2.46 

Lime  (CaO) 0 . 53 

Magnesia  (MgO) 0.71 

Potash  (K2O) 2 .  SO 

Soda  (Na2O) 0.43 

Water  (H2O) 7 . 01 

Total.. 100.82 

In  one  case  the  green  clay  showed  a  total  of  2.15  per  cent  of  ferric 
oxide,  of  which  0.88  per  cent  was  soluble  in  acid.  The  flashed  surface 
of  a  brick  made  from  this  clay  gave,  on  analysis,  a  total  of  2.31  per  cent 
of  ferric  oxide,  of  which  0.14  per  cent  was  soluble  in  nitro-hydrochloric 
acid,  thus  indicating  that  during  the  burning  most  of  the  iron  oxide  had 
combined  with  silica,  forming  a  ferrous  silicate. 

2.  The  temperature  reached  must  be  sufficient  to  cause  a  combination 
of  the  iron  and  silica,  and,  therefore,  it  varies  with  different  clays,  the 
combination  being  aided  by  the  presence  of  fluxes. 

If  the  kiln  atmosphere  is  oxidizing  during  nearly  the  entire  burning,, 
with  only  a  small  period  of  reduction  at  the  end,  the  temperature  reached 
must  be  comparatively  high  in  order  to  insure  union  of  the  iron,  and 
silica  by  fusion.  If,  however,  a  reducing  fire  is  maintained  during  most 
of  the  burning,  then  the  temperature  need  not  be  as  high,  because  the 
clay  will  vitrify  sooner.  (See  Fusibility,  Chapter  III.) 

At  one  factory  it  had  formerly  been  the  practice  to  burn  with  an 
oxidizing  fire  to  a  high  temperature,  namely,  from  cone  11-12,  and  then 
to  cause  reducing  conditions  to  take  place  in  the  kiln  during  the  last 
five  or  six  hours  of  the  burn.  This  practice,  however,  was  changed, 
it  being  found  that  by  maintaining  a  reducing  fire  during  the  entire 
period  following  water  smoking  a  lower  temperature  was  sufficient. 

3.  The  oxidation  which  causes  the  flashing  probably  takes  place  in 
the  first  twelve  hours  after  closing  the  kiln,  and  can  be  regulated  by  a 
proper  handling  of  the  dampers. 

In  the  experiments  of  Bleininger,  already  referred  to,  it  was  found 
that  a  reduction  of  air,  equal  to  20  per  cent  below  that  required  for 
ideal  oxidation  and  considered  as  100,  is  usually  sufficient  to  produce 
flashing. 


KINDS   OF  CLAYS 


191 


By  this  is  meant  that  "100  per  cent  of  air  represents  theoretically 
ideal  conditions,  in  which  just  enough  air  is  present  to  consume  all  the 
combustible  gases  forming  CO2;  less  than  100  per  cent  of  air  corresponds 
to  reducing  conditions.  For  instance,  if  an  analysis  on  calculation 
represents  90  per  cent  of  air,  it  tells  us  that  the  gases  are  reducing  to  the 
extent  of  10  per  cent  of  air;  similarly,  110  per  cent  shows  an  excess  of 
air  to  the  amount  of  10  per  cent." 

While  100  per  cent  represents  theoretically  the  amount  of  air  required 
for  perfect  combustion,  still  in  actual  practice  with  coal-fuel  the  mixture 
of  gases  is  not  perfect,  and  it  may  be  necessary  to  have  more  than  100 
per  cent  of  air  present  to  bring  about  thorough  oxidation. 

.4.  As  regards  the  rate  of  cooling,  it  was  found  that  the  longer  the 
period  of  cooling  from  the  maximum  temperature  down  to  approximately 
700°  C.  the  darker  the  flash  under  given  conditions. 

Enameled  brick. — The  clays  used  for  these  are  similar  to  those  em- 
ployed in  the  manufacture  of  buff  pressed  brick.  The  enamel  is,  of 
course,  an  artificial  mixture,  but  must  conform  to  the  clay  body  to 
avoid  cracking  or  scaling  off  of  the  coat. 

Paving-brick  Clays 

A  considerable  variety  of  materials  is  used  for  paving-brick  manu- 
facture, ranging  from  common  surface-clays  to  semi-refractory  ones, 
but  those  most  frequently  employed  are  impure  shales,  these  being 
often  found  to  give  the  desired  vitrified  body  at  not  too  high  a  tempera- 
ture. Shales  of  this  character  have  a  wide  geographical  and  geological 
distribution,  but  those  most  extensively  worked  are  in  the  Carboniferous 
of  Ohio,  Pennsylvania,  Indiana,  and  Illinois.  In  New  York  and  Mary- 
land Devonian  shales  have  yielded  excellent  results,  and  in  the  Western 
States,  such  as  Colorado,  the  Cretaceous  shales  are  of  importance  in  this 
connection. 

Wheeler  l  gives  the  following   range  of  composition  of  paving-brick 

clays: 

RANGE  OF  COMPOSITION  OF  PAVING-BRICK  CLAYS 


Mini- 
mum. 

Maxi- 
mum. 

Average. 

Silica  (SiO  )                          .  .            

49.00 

75.00 

56.00 

Alumina  (A12O3).        

11.00 

25.00 

22.50 

Ferric  oxide  (Fe2O3)  

2.00 

9.00 

6.70 

Lime  (CaO)                                                           

.20 

3.50 

1  20 

Magnesia  (MsrO)                                         

.10 

3  00 

1  40 

Alkalies  (Na  O  K  O)                            

1.00 

5.50 

3  70 

Ignition   loss                                         

3.00 

13.00 

7.00 

1  Mo.  Geol.  Surv.,  XI,  p.  456,  1896. 


192  CLAYS 

Williams l  gives  the  following  limits  between  which  the  different 
ingredients  of  Iowa  paving-brick  clays  range: 

RANGE  OF  COMPOSITION  OF  IOWA  PAVING-BRICK  CLAYS 

Maxirmim,     Minimum, 
per  cent.        per  cent. 

Silica  (SiO2) 74 . 58  58 . 56 

Alumina  (A12O 3) 22.33  8.28 

Ferric  oxide  (Fe2O3) 5.75  2.88 

Lime  (CaO) 3.42  1.55 

Magnesia  (MgO) 3.47  1.22 

Potash  (K2O) 1.15  .29 

Soda  (Na2O) 1 .79  1 .08 

Water  (H2O) 5.33  1.07 

Carbon  dioxide  (CO2) 2.23  1 .73 

Sulphur  trioxide  (SO3) 1 . 85  1 . 28 

Moisture 1.13  .28 

The  analyses  show  a  rather  high  percentage  of  total  fluxes. 

Clays  for  paving  brick  should  possess  fair  plasticity,  since  they  are 
commonly  molded  by  the  stiff-mud  process;  they  should  have  good 
tensile  strength,  and  a  range  of  not  less  than  250°  F.  between  the  points 
of  incipient  vitrification  and  viscosity. 

Fireproofing  and  Hollow-brick  Clays 

The  clay  used  for  making  hollow  bricks  and  fireproofing  vary  with 
the  locality.  At  not  a  few  yards  where  red  bricks  are  manufactured 
the  red-burning  surface-clays  of  Pleistocene  age  are  employed.  In 
New  Jersey,  where  many  thousand  tons  are  annually  produced  to  supply 
the  New  York  and  other  large  Eastern  markets,  a  mixture  of  red-burning 
sandy  clay  and  a  small  amount  of  lowr-grade  fire-clay  are  chosen,  while 
in  the  States  of  the  Eastern  and  Central  coal-measure  areas,  as  in  Pennsyl- 
vania, Ohio,  Indiana,  and  Illinois,  Carboniferous  shales  are  widely  used. 

It  is  therefore  difficult  to  lay  down  any  fixed  set  of  requirements  for 
the  raw  materials  of  this  class.  This  much  can  be  said:  They  should 
have  sufficient  plasticity  to  flow  smoothly  through  the  peculiar  shape 
of  die  used  in  making  them;  they  should  also  possess  fair  tensile  strength; 
burn  to  a  good  hard  but  not  vitrified  body  at  a  comparatively  low  cone. 
Concretionary  masses,  if  present,  should  be  either  removed  or  crushed. 

The  following  analyses  show  well  the  composition  of  clays  or  shales 
used  for  this  kind  of  ware: 

1  la.  Geol.  Surv.,  XIV,  p.  229,  1904. 


KINDS  OF  CLAYS  193 

ANALYSES  OF  CLAYS  USED  FOR  HOLLOW  BRICK  AND  FIREPROOFING 


I. 

11. 

III. 

Silica  (SiO2)     . 

52.22 
29.43 

2.78 

57.57 
21.70 
2.26 
4.11 

51.95 
18.34 
7.56 

Alumina  (A12O3).                .        

Ferric  oxide  (Fe2O3)  

Ferrous  oxide  (FeO)  

Lime  (CaO)  

.88 
.72 
2.10 
.75 

.32 
1.12 
2.16 
.33 
1.10 

4.14 
3.36 
1.43 
2.69 

Magnesia  (MsrO) 

Pot'ash  (K2O) 

Soda  (Na  O) 

Titanium  "oxide  (TiO.)  

Water  (H2O)                                                                            1 

11.10 

/    6.78 
1  

7.39 
.42 

Moisture                                                                                    / 

Carbon  dioxide  (CO2).  .             .  .              

Sulphur  trioxide  (SO3).  .           

2.76 

Final  Report,  VI,  p.  282,  1904. 
eol.  and  Nat.  Res.,  29th  Ann. 

II.   Underclay  beneath  Coal  II,  Cannelton,  Ind.     Ind.  Dept.  G 

Rept.,  p.  338,  1904. 
III.   Representative  shale-clay  from  Iowa. 


la.  Geol.  Surv.,  XIV,  p.  232,  1904. 


The  physical  tests  of  fireproofing  clays  shown  on  page  194  are  given 
in  the  New  Jersey  Geological  Survey  report.1 

The  tabulation  is  not  without  interest,  and  shows  a  considerable 
variation  in  certain  directions.  The  air-shrinkage  shows  little  variation, 
but  the  tensile  strength  shows  a  great  range.  Of  these  different  samples, 
Nos.  1,  2,  and  6  are  practically  from  the  same  bed.  No.  5  is  from  the 
base  of  the  Raritan  series,  and  is  one  of  the  most  dense-burning  clays  to 
be  found  in  that  section  or  even  New  Jersey.  Most  of  these  clays  have 
to  be  burned  to  cone  01  before  becoming  steel-hard,  the  one  exception 
being  No.  5,  which  burns  very  hard  at  cone  05.  They  all  burn  red. 
The  pyrite  and  limonite  nodules  are  abundant  in  some  of  the  layers,  and 
in  burning  often  fuse,  swell,  and  spall  off  pieces  of  the  ware. 

Slip-clays 

A  slip-clay  is  one  containing  such  a  high  percentage  of  fluxing  im- 
purities, and  of  such  texture  that  at  a  low  cone  it  melts  to  a  greenish  or 
brown  glass,  thus  forming  a  natural  glaze.  It  must  be  fine  grained, 
free  from  lumps  or  concretions,  show  a  low  air-shrinkage,  and  mature 
in  burning  at  as  little  above  cone  5  as  possible. 

While  easily  fusible  clays  are  not  uncommon,  all  do  not  melt  to  a  good 
glaze. 

"A  good  slip-clay  makes  a  glaze  which  is  free  from  defects  common 
to  artificial  glazes.  It  will  fit  a  wide  range  of  clays,  and  since  it  is  a 

1  N.  J.  Geol.  Surv.,  Final  Kept.,  VI,  p.  280,  1£04. 


194 


CLAYS 


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KINDS   OF  CLAYS 


195 


natural  clay  it  will  undergo  the  same  changes  in  burning  as  the  body 
on  which  it  is  placed.  Artificial  mixtures  of  exactly  similar  composition 
to  the  natural  clays  have  failed  to  give  the  excellent  results  as  to  gloss 
or  color  that  are  attained  by  the  natural  clay."  1 

While  several  fair  slip-clays  have  been  found  in  different  parts  of  the 
country,  none  have  given  thorough  satisfaction  except  the  Albany, 
N.  Y.,  material,  which  is  shipped  to  all  parts  of  the  United  States  for 
potters'  use. 

In  applying  the  glaze  to  the  ware  the  clay  is  mixed  with  water  to  a 
creamy  consistency  and  applied  to  the  ware  either  by  dipping  or  spraying. 
Attempts  have  sometimes  been  made  to  lower  the  fusing-point  of  the 
slip  by  the  addition  of  fluxing  oxides. 

The  following  are  analyses  of  slip-clays: 

ANALYSES  OF  SLIP-CLAYS 


I. 

II. 

III. 

IV. 

V. 

Silica  (SiO2)     .            

55  .  60 

43.94 

63.63 

38.08 

57.01  . 

Alumina  (A12O3)  

14.80 

11.17 

13.57 

11.36 

11.85 

Ferric  oxide  (Fe2O3)  

5.80 

3.81 

7.77 

2.60 

3.02 

Lime  (CaO)  

5.70 

11.64 

2.55 

23.70 

9.56 

2.48 

4.17 

1.47 

tr. 

1.20 

Potash  (K2O)  

3.23 

2.90 

2.63 

.58 

.75 

Soda  (Na2O)  

1.07 

.71 

.88 

1.60 

2.01 

.14 

Titanium  oxide  (TiO2)     .               .  . 

.70 

1.13 

Phosphorus  pentoxide  (P  O  ) 

15 

Water  (H2O).                 .               

5.18 

3.90 

4.75 

3.06 

4.00 

Carbon  dioxide  (CO2)  and  moisture.  .  .  . 

4.94 

15.66 

2.90 

18.80 

8.00 

Total  .  .                      

98.09 

98.00 

100.15 

100.48 

98.53 

I.  Albany,  N.  Y.     Ohio  Geol.  Surv.,  VII,  p.  105,  1893. 
II.  Rowley,  Mich.     Ibid.,  p.  105. 

III.  Brimfield,    O.     Ibid.,    p.    105. 

IV.  Leon  Creek  near  San  Antonio,  Tex.     O.  H.  Palm,  anal. 

V-  Alazan  Creek  near  San  Antonio,  Tex.     O.  H.  Palm,  anal. 

The  use  of  slip-clays  for  glazing  stoneware  is  decreasing  each  year, 
because  an  artificial  white  glaze  is  now  usually  preferred. 

MISCELLANEOUS    KINDS    OF   CLAYS 

Clays  Used  when  Burned 

Gumbo-clay. — Under  this  name  there  are  included  certain  fine- 
grained, highly  plastic,  tenacious  clays  of  surface  character,  which  are 
found  at  many  points  in  the  Western  Central  States.  Their  high  shrinkage 


1  la.  Geol.  Surv.,  XIV,  p.  224,  1904. 


196  CLAYS 

and  dense  character  prohibits  their  use  for  brickmaking,  but  they  are 
found  excellently  adapted  to  the  manufacture  of  railroad  ballast. 

Wheeler,  in  describing  the  Missouri  occurrences,1  states  that  they 
do  not  differ  chemically  from  common  brick,  paving  brick,  sewer-pipe 
or  other  burnt  clays,  and  "  their  peculiar  value  for  burnt  ballast  is  entirely 
a  physical  one."  He  gives  the  following  variation  in  composition: 

Silica  (SiO2) 55    -65 

Alumina  (A12O3). 15     -20 

Ferric  oxide  (Fe2O3) 5     -7 

Lime  (CaO) 1     -3 

Magnesia  (MgO) 5-2 

Alkalies  (Na2O,K2O) 2.5-4 

Water  (H2O) 6     -10 

Fluxes 10     -15 

Their  physical  properties  range  as  below : 

Water  required 22-25  per  cent. 

Average  tensile  strength 270-410  Ibs.  per  sq.  in. 

Air-shrinkage 8-10  per  cent. 

Fire-shrinkage 1-6  per  cent. 

Incipient  vitrification 1600°-1700°  F. 

Complete  vitrification 1750°-1850°  F. 

Viscosity 1900°-2000°  F. 

Retort-clay. — A  dense-burning,  plastic,  semi-refractory  clay  used 
chiefly  in  the  manufacture  of  gas-retorts  and  zinc-retorts.  In  New 
Jersey  the  term  is  often  applied  to  stoneware-clays. 

Pot-clay. — A  clay  used  for  the  manufacture  of  glass  pots,  and  conse- 
quently representing  a  very  dense-burning  fire-clay.  In  refractoriness 
it  ranges  from  a  highly  refractory  to  a  refractory  clay. 

Ware-clay. — A  term  sometimes  used  for  ball-clays,  especially  in  the 
Woodbridge,  N.  J.,  district. 

Pipe-clay. — This  is  a  term  applied  to  almost  any  fine-grained  plastic 
clay.  Strictly  speaking,  it  would  refer  to  a  clay  used  for  making  sewer- 
pipe. 

Sagger-clay. — This  is  a  term  applied  to  clays  which  are  used  in  a 
mixture  for  making  the  saggers  in  which  the  white  ware  and  other 
high  grades  of  pottery  are  burned.  They  are  commonly  rather  siliceous 
in  their  character,  although  some  may  be  used  on  account  of  their  bonding 
power  and  freedom  from  grit  to  hold  the  more  porous  grades  together. 
As  far  as  the  physical  properties  go  the  sagger-clays  are  not,  therefore, 
represented  by  any  one  type.  Their  refractoriness  varies  from  that 
of  a_  refractory  to  a  semi-refractory  clay. 
1  Mo.  Geol.  Surv.,  XI,  p.  542,  1896.  See  also  la.  Geol.  Surv.,  XIV,  p.  534,  1904. 


KINDS  OF  CLAYS  197 

Wad-clay. — This  is  a  low  grade  of  fire-clay,  which  is  used  for  grouting 
the  joints  between  the  saggers  when  they  are  set  up  in  bungs  in  the 
kilns. 

Portland-cement  clay. — The  use  of  clay  or  shale  for  Portland  cement 
is  the  most  important  of  what  may  be  termed  the  minor  uses  of  clay. 
Portland  cement  is  essentially  an  artificial  mixture  of  lime,  silica,  and 
alumina.  The  first  of  these  is  usually  supplied  by  some  form  of 
calcareous  material,  such  as  limestone,  marl,  or  chalk,  while  the  other 
two  are  obtained  by  the  selection  of  clay  or  shale,  the  mixture  con- 
sisting approximately  of  75  per  cent  lime  carbonate  and  25  per  cent 
clay  or  shale. 

Clays  or  shales  to  be  used  for  Portland-cement  manufacture  should 
be  as  free  as  possible  from  coarse  particles  or  lumps  of  sand,  gravel,  or 
concretions.  These  conditions  are  best  met  by  the  transported  clays, 
since  residual  clays  are  frequently  sandy  or  stony,  and  many  glacial 
clays  notably  so.  An  examination  of  the  analyses  of  clays  used  at 
different  works  in  this  country  shows  that  the  silica  percentage  ranges 
from  50  to  70  per  cent;  when  calcareous  clays  are  used  it  may  fall  below 
50  per  cent. 

The  analyses  shown  on  page  198  give  the  composition  of  clays  em- 
ployed at  a  number  of  different  localities. 

It  is  not  to  be  understood  from  what  has  been  said  above  that  the 
clays  whose  analyses  are  given  can  be  used  only  for  Portland-cement 
manufacture;  indeed  nearly  all  of  them  could  be  utilized  for  some  kind 
of  clay  product. 

Clays  Used  in  Unburned  Condition 

Paper-clays. — These  form  a  type  of  clay  much  used  by  paper  manu- 
facturers, and  which  are  mixed  in  with  the  pulp  fiber,  so  that  the  latter 
can  enmesh  a  certain  amount  of  the  clay  particles.  The  degree  of  plasticity 
of  the  clay  seems  to  play  an  important  role,  since  it  is  found  that  a  given 
paper  will  often  retain  a  much  greater  proportion  of  some  clays  than 
others,  those  of  which  the  greatest  quantity  is  retained  being  the  most 
plastic.  Sand  is  an  undesirable  constituent  of  paper-clay,  for  the  reason 
that  the  sand-grains  wear  the  wires  of  the  screens  through  which  the 
materials  have  to  pass.  It  can  often  be  eliminated  from  the  clay  by 
washing.  Whiteness  of  color  is  a  third  essential,  and  must  be  a  primary 
character  of  the  clay. 

The  best  grades  of  paper-clay  are  some  imported  washed  kaolins, 
but  large  quantities  of  good  paper-clay  are  also  obtained  from  the  Potomac 
formations  of  Georgia,  and  the  Cretaceous  and  Tertiary  ones  of  South 


198 


CLAYS 

ANALYSES  OF  PORTLAND-CEMENT  CLAYS 


I. 

II. 

III. 

IV. 

V. 

VI. 

Silica  (SiOs)  
Alumina  (A12O3) 

53.30 
23.29 
9.52 
.36 
1.49 
1.36 
2.76 

63.73 
22.12 
9.01 
2.83 

}•>• 

74.29 
12.06 
4.92 
.41 
.68 
f       .76 
1     1.80 

64.85 
17.98 
5.92 
2.24 
1.40 

55.27 
10.20 
3.40 
9.12 
5.73 

40.56 

8.52 
2.84 
20.94 
1.32 

}    1.97 

Ferric  oxide  (Fe2O3)  
Lime  (CaO)  .            .... 

Magnesia  (MgO)  

Potash  (K2O)  

Soda  (Na2O)             .  .    . 

Sulphur  trioxide   (SO3)  .  . 

Caibon  dioxide  (CO2).  .  . 

}    4.98 

{:••••• 

17.  €0 
5.95 

Water  (H2O)  

5.16 

VII. 

VIII. 

IX. 

X. 

XI. 

Silica  (SiO2) 

57.98 
18.26 
4.57 
1.75 
1.83 

61.09 
19.19 
6.78 
2.51 
.65 
1.8 

54.30 
19.33 
5.57 
3.29 
2.57 

61.92 
16.58 

7.84 
2.01 
1.58 

1    3.64 

tr. 

55.27 

}  28.15 

5.84 
2.25 

.12 

Alumina  (Al2Oo)                 .... 

Ferric  oxide  (Ft^O^  .        ... 

Lime  (CaO)        

Magnesia  (MgO)  

Potash  (K2O)     

Soda  (Na  O)             

1.36 

Sulphur  trioxide  (SOg)  
Carbon  dioxide  (CO2)  

1.28 
|  12.08 

1.42 
5.13 

2.36 

Water  (H2O)           

I.  Little  Rock,  Ark.     Amer.  Inst.  Min.  Eng.,  Trans.,  XXVII,  62. 

II  Santa  Cruz,  Cal.     Min.  Indus.,  I,  p.  52. 

III.  Bedford,  Ind.     Ind.  Dept.  Geol.  and  Nat.  Res.,  25th  Ann.  Rept.,  p.  328. 

IV.  Millbury,  O.     Mich.  Geol.  Surv.,  VIII,  Pt.  Ill,  p.  229. 

V.  Syracuse,  Ind.     Ind.  Dept.  Geol.  and  Nat.  Res.,  25th  Ann.  Rept.,  p.  28. 

VI.  Bristol,  Ind.     U.  S.  Geol.  Surv.,  21st  Ann.  Rept.,  Pt.  6  (ctd.),  p.  400. 

VII.  Yankton,  S.  Dak.     Min.  Indus.,  VI,  p.  97. 

VIII.  Alpena,  Mich.     Mich.  Geol.  Surv.,  VIII,  Pt.  Ill,  p.  227. 

IX.  La  Salle,  111.      U.  S.  Geol.  Surv.,  20th  Ann.  Rept.,  Pt.  6  (ctd.),  p.  544. 

X.  Catskill,  N.  Y.      Supplied  by  company. 

XI.  Glens  Falls,  N.  Y.     Min.  Indus.,  VI,  p.  97. 


Carolina.  The  Algonkian  kaolins  of  Maryland,  Delaware,  and  Connecticut, 
as  well  as  the  white  residual  Cambro-Silurian  ones  of  southeastern 
Pennsylvania,  have  also  been  used  for  this  purpose. 

Many  of  these  clays  are,  however,  also  utilized  for  the  manufacture  of 
clay-products,  such  as  white  earthenware,  wall-tile,  etc. 

Mineral  paint. — Certain  clays  and  shales,  when  ground  and  mixed 
with  oil,  make  a  good  grade  of  mineral  paint.  Their  color  in  most 
cases  is  due  to  some  form  of  iron  oxide,  or  more  rarely  manganese. 
Ocher  is  often  nothing  more  than  a  fine-grained  ferruginous  clay  colored 
by  limonite,  and  the  same  may  be  true  of  sienna. 

Mineral  paints  made  from  clays  and  shales  form  a  cheap  and  satisfac- 
tory form  of  pigment  for  application  to  wooden  surfaces.  The  value 
cf  the  material  depends  to  a  large  extent  on  the  shade  of  color,  its  texture, 


KINDS  OF  CLAYS  199 

and  the  amount  of  oil  that  has  to  be  mixed  with  it  in  order  to  get  the 
proper  degree  of  fluidity. 

Ultramarine  manufacture. — Washed  kaolin  or  even  very  fine-grained 
white  sedimentary  clays  are  used  in  the  manufacture  of  ultramarine  to 
serve  as  a  nucleus  for  gathering  the  coloring  material.  For  this  work 
the  clay  should  be  as  low  in  iron  or  lime  as  possible,  and  an  excess  of 
silica  is  undesirable. 

Polishing  and  abrasive  materials. — Many  clays  exert  a  combined 
polishing  and  abrasive  action,  on  account  of  the  very  finely  divided  grains 
of  sand  which  they  contain.  The  well-known  Bath  brick  which  has 
such  an  extensive  domestic  use  for  scouring  steel  utensils  is  simply  a 
fine-grained  siliceous  clay,  which  is  deposited  during  high  tide  along 
the  banks  of  the  Parrot  River  in  England. 

Some  clay  is  used  for  bonding  purposes  in  the  manufacture  of 
corundum-wheels.  These  are  burned  before  use,  so  that  the  clay  vit- 
rifies and  holds  the  corundum-grains  together. 


METHODS  OF  MINING  AND  MANUFACTURE 

METHODS    OF   MINING 

Prospecting  for  Clays 

A  knowledge  of  the  facts  given  in  Chapter  I  will,  if  borne  in  mind, 
be  of  much  aid  to  the  clay-worker  in  prospecting  for  clays,  but  several 
additional  points  may  be  mentioned  by  which  beds  of  clay  may  be 
located. 

Outcrops. — The  presence  of  a  clay-bed  is  usually  detected  by  means 
of  an  outcrop.  These  exposures  are  commonly  to  be  found  on  inclined 
surfaces,  such  as  hilltops,  or  where  natural  or  artificial  cuts  have  been 
made.  The  washing  out  of  gullies  by  heavy  rains,  the  cutting  of  a 
stream  valley,  railroad  or  wagon-road  cuts,  all  form  good  places  in 
which  to  look  for  outcropping  clay-beds.  The  newer  the  cut  the  better 
the  exposure,  for  the  sides  of  such  excavations  wash  down  rapidly,  and 
a  muddy-red  surface-clay  or  loam  will  often  run  down  over  a  bed  of 
lighter  colored  clay  beneath  so  as  to  completely  hide  it  from  view.  If 
the  cut  is  deep  and  freshly  made  the  depth  of  weathering  can  frequently 
be  determined. 

Springs. — In  many  cases  the  presence  of  clay  is  shown  by  the  occur- 
rence of  one  or  more  springs  issuing  from  the  same  level  along  some 
hill-slope.  These  are  caused  by  waters  seeping  down  from  the  surface 
(Fig.  38)  until  they  reach  the  top  of  some  impervious  clay  stratum, 


200 


CLAYS 


which  they  then  follow  to  the  face  of  the  bank  where  they  issue.     The 
presence  of  springs,  however,  cannot  be  used  as  a  positive  indication  of 


—  —  _    — __  _        -  •    _  —  — \  Spring 


_ 


\ 


FIG.  38. — Formation  of  spring  due  to  ground-water  following  a  clay-layer. 

clay,  for  a  bed  of  cemented  iron  sand,  or  even  dense  silt,  may  produce  the 
same  effect  (Fig.  39). 


FIG.  39.— Formation  of  spring  due  to  a  layer  of  cemented  sand. 

Ponds. — In  many  regions  covered  by  glacial  drift,  pools  of  water  are 
often  retained  in  depressions,  because  of  the  presence  below  of  a  water- 
tight bed  of  clay  (Fig.  40).  It  does  not  necessarily  indicate  a  thick 


*~-^l^riviwi:"~-"-- -^^^ 
FIG.  40. — Formation  of  a  pond  due  to  a  clay-bed  beneath  a  depression. 

deposit,  for  a  very  thin  layer  often  holds  up  a  considerable  body  of  water. 
Such  ponds  may  likewise  in  rarer  instances  be  caused  by  ground-water 
seeping  down  from  higher  levels,  even  in  the  absence  of  clay. 

Vegetation. — Clay-deposits  in  some  areas  produce  a  different  type 
of  plant  growth  from  other  soils,  but  the  character  of  the  vegetation 
can  only  be  used  as  a  subordinate  aid  in  the  search  of  clay. 


PLATE   VIII 


Showing  method  of  working  clay  in  a  rectangular  pit.     (After  Ries,  N.  J.  Geol. 
Surv.,  Fin.  Kept.,  VI,  p.  34,  1904.) 

201 


KINDS  OF  CLAYS  203 


EXPLOITATION   OF    CLAY-DEPOSITS 

The  location  of  a  clay-deposit  is  followed  by  a  determination  of 
its  thickness,  extent,  character,  and  uses.  The  first  two  points  and 
some  facts  bearing  on  the  third  are  determined  in  the  field;  the 
behavior  of  the  clay  when  mixed  up  and  burned  is  found  out  by  tests 
made  in  the  laboratory  or  at  some  factory,  and  the  information  thus 
obtained  indicates  the  commercial  value  of  the  material. 

To  determine  the  thickness  and  extent  of  the  deposit  a  careful 
examination  should  be  made  of  all  clay  outcrops  in  neighboring  gullies, 
or  other  cuts  on  the  property  having  the  clay.  Since,  however,  most 
clay-slopes  wash  down  easily,  it  may  be  necessary  to  dig  ditches  from 
the  top  to  the  bottom  of  the  cut  or  hillside  in  order  to  uncover  the  undis- 
turbed clay-beds.  In  most  cases,  however,  the  cuts  are  not  sufficiently 
close  together  and  additional  means  have  to  be  taken  to  determine 
the  thickness  of  the  deposit  at  intermediate  points.  Such  data  are 
sometimes  obtainable  from  wells  or  excavations  made  for  deep  cellars, 
but  the  information  thus  obtained  has  to  be  taken  on  hearsay.  Borings 
made  with  an  auger  furnish  a  more  satisfactory  and  rapid  means  of 
determining  the  thickness  of  the  clay-deposit  away  from  the  outcrop: 
A  post-hole  auger,  cutting  a  hole  of  three  to  four  inches  diameter,  can 
easily  be  used  to  a  depth  of  30  or  40  feet,  while  one  of  two  inches  diameter 
can  be  sunk  to  100  feet  without  much  difficulty. 

From  comparison  of  the  data  obtained  from  the  bore-holes  and 
outcrops,  any  vertical  or  horizontal  variations  in  the  deposit  can  usually 
be  traced.  Limonite  concretions  or  crusts,  if  present  in  any  abundance, 
are  almost  sure  to  be  discovered,  and  even  the  dryness  of  the  beds  can  be 
ascertained.  Variations  in  the  thickness  of  the  bed  and  amount  of 
stripping  are  also  determinable.  If  small  samples  are  desired  for  labora- 
tory testing  these  can  be  taken  from  the  outcrops  and  bore-holes,  but  if 
large  samples  are  wanted  from  the  intermediate  points  it  is  best  to  sink 
test-pits  where  the  borings  were  made. 

In  some  regions  the  clay-miners  make  use  of  an  auger  to  guide  them 
in  their  digging  operations,  this  being  often  necessary  on  account  of 
the  rapid  variations  that  may  occur  in  any  one  deposit. 

Adaptability  of  Clay  for  Working 

Having  determined  the  thickness,  extent,  and  character  of  the  clay 

there  still  remain  several  important  points  which  have  to  be  considered. 

One  of  these  is  the  amount  of  stripping,  for  if  the  clay  is  not  of  high 


204  CLAYS 

grade  it  will  not  pay  to  remove  much  overburden  unless  the  latter  can 
be  used.  It  is  sometimes  utilized  for  filling,  where  the  factory  is  to  be 
erected  next  to  the  bank,  or  for  admixture  with  the  clay,  especially  if 
the  latter  is  too  plastic  or  fat.  In  such  event,  ho\vever,  the  overburden 
should  be  free  from  pebbles,  or  if  not  it  should  be  screened.  Frequent 
neglect  of  this  often  injures  the  bricks.  If  the  overburden  is  clean  sand 
it  can  often  be  disposed  of  for  foundry  use,  building  or  other  puiposes. 

Drainage  facilities  must  be  looked  out  for,  since  dryness  is  essential 
for  successful  and  economic  working  of  the  clay-bed.  In  some  districts 
the  clay  is  underlain  by  a  stratum  of  wet  sand,  which  should  not  be  pene- 
trated. In  rare  cases  an  underlying  sand-bed  is  dry  and  may  even  serve 
for  drainage  purposes.  If  the  clay-deposit  lies  below  the  level  of  the 
surrounding  country,  drainage  will  be  more  difficult  than  where  the  bed 
outcrops  on  a  hillside,  although  in  the  latter  case  trouble  may  be  and 
often  is  caused  by  springs. 

Some  banks  contain  several  different  grades  of  clay,  and  it  then  remains 
to  see  whether  they  are  all  of  marketable  character,  or,  if  not,  whether 
the  expense  of  separating  the  worthless  clay  will  overbalance  the  profit 
derived  from  the  salable  earth. 

Transportation  facilities  are  not  to  be  overlooked,  either  for  the  raw 
clay  or  for  the  product,  where  the  factory  is  located  at  the  pit  or  bank. 
Long  haulages  with  teams  are  costly,  and  steam  haulage  is  far  more 
economical  when  the  output  warrants  it;  but,  even  with  the  establish- 
ment of  favorable  conditions  in  every  case,  the  successful  marketing  of 
the  product  is  sometimes  a  long  and  tedious  task,  for  many  manufacturers 
hesitate  to  experiment  with  new  clays. 

Methods  of  Winning  the  Clay 

Clays  and  shales  are  commonly  worked  either  as  open  pits  or  quarry 
workings  or  by  underground  methods.  The  open-pit  method  is  practised 
at  most  localities  where  the  deposit  lies  at  or  near  the  surface  and  there 
is  little  or  no  overburden  to  be  removed.  If  the  clay  is  soft  and  the  quan- 
tity to  be  dug  small  picks  and  shovels  are  commonly  used,  but  for  more 
extensive  operations  plows  and  scrapers  are  cheaper  and  of  greater 
capacity.  In  extensive  works  steam-shovels  (PL  XXVI,  Fig.  1)  are  the 
best  and  most  economical  means,  and  capable  of  excavating  even  soft 
shales.  They  can  be  used  with  a  face  of  15  or  20  feet  height,  but  have 
the  disadvantage  of  mixing  the  clay  from  the  top  to  the  bottom  of  the 
bank. 

In  deposits  of  very  tough  clay  or  hard  shale  blasting  is  frequently 


OF   THf 

UNIVERSITY 

KINDS  OF  CLAYS  .  205 


, 

. 

X^'jro_R 


necessary  in  order  to  loosen  up  the  material.  Since  surface-waters 
often  trickle  through  the  soil  until  they  reach  a  clay-surface  and  follow 
it,  there  is  not  infrequently  a  series  of  small  springs  emerging  along  the 
top  of  a  clay-bank,  and  the  water  from  these  is  usually  diverted  by  means 
of  properly  constructed  ditches.  In  addition  to  these  ditches,  however, 
it  is  commonly  necessary  to  have  additional  ones  on  the  ground  at  the 
base  of  the  bank.  If  the  bank  is  high,  that  is  seventy-five  feet  or  more 
and  of  soft  clay,  it  is  safer  to  work  it  in  several  benches  or  steps  (PL 
XXXIII,  Fig.  2)  and  not  as  a  vertical  face,  for  the  latter  will  be  apt  to 
slide  if  the  clay  gets  water-soaked.  Neither  should  the  factory  be  located 
close  to  the  base  of  such  a  bank,  where  there  is  danger  of  slides,  and  the 
writer  has  seen  several  instances  in  which  yards  have  been  buried  in 
this  manner.  The  ease  with  which  large  masses  of  clay  will  sometimes 
cave  or  slide  when  softened  with  water  was  well  illustrated  recently  at 
Haverstraw,  N.  Y.,  when  a  portion  of  a  large  cliff  overlooking  the  clay- 
pits  sank  down,  carrying  many  houses  and  people  with  it. 

Where  the  clay  is  not  of  uniform  quality  from  top  to  bottom,  or 
when  a  number  of  layers  of  different  kinds,  as  terra-cotta,  fire-,  and  stone- 
ware-clay are  present,  it  is  then  necessary  to  strip  off  each  one  separately 
and  place  it  in  a  storage  pile  by  itself.  This  is  notably  the  custom  in 
the  Woodbridge  and  Perth  Amboy  districts  of  New  Jersey,  and  the 
practice  followed  there  may  be  described  in  some  detail,  as  the  same 
method  might  be  adopted  in  other  parts  of  the  coastal  plain  area. 

In  the  area  referred  to  the  better  grades  of  clay  are  generally  dug  by 
small  pits.  These  are  commonly  square,  and  about  ten  to  fifteen  feet 
or  more  on  a  side  (Fig.  41),  and  the  depth  is  usually  that  of  the  thickness 
of  the  good  clay  in  the  bed.  Around  Woodbridge  the  miners  commonly 
penetrate  the  No.  1  fire-clay  or  sometimes  the  extra  sandy  clay  below,  but 
the  depth  is  oftentimes  determined  by  the  character  of  the  ground  "and 
presence  or  absence  of  water  underneath.  Where  there  is  danger  of 
the  pit  caving  in,  the  sides  are  sometimes  protected  in  the  weak  parts 
by  planking,  held  in  place  by  cross-timbers. 

The  clay  is  dug  by  a  gouge-spade,  which  differs  from  an  ordinary 
spade  in  having  a  curved  or  semi-cylindrical  blade,  as  well  as  a  tread  on 
its  upper  edge,  to  aid  the  digger  in  forcing  it  into  the  tough  clay.  A 
lump  of  clay  dug  by  the  pitman  is  termed  a  spit,  and  in  taking  out  the 
material  it  is  customary  to  dig  over  the  area  of  the  bottom  of  the  pit 
to  the  depth  of  a  spade  and  then  begin  a  new  spit.  The  thickness  of  any 
bed  of  clay,  therefore,  is  always  judged  in  spits. 

Where  a  pit  is  dug  so  deep  that  it  is  not  possible  for  the  workman 
to  throw  or  lift  the  lumps  to  the  surface  of  the  ground,  a  platform  may 


206 


CLAYS 


be  built  in  the  pit  half-way  up  its  side,  or  else  the  clay  is  loaded  into 
buckets  (PL  V1I1)  and  hoisted  to  the  surface  by  means  of  a  derrick 
operated  by  steam-  or  horse-power.  As  soon  as  a  pit  is  worked  out  a 
new  one  is  begun  next  to  it,  but  a  wall  of  clay,  1  to  2  feet  thick,  is  com- 
monly left  between  the  two.  When  the  second  pit  is  done  as  much  as 
possible  of  this  wall  is  removed.  A  platform  of  planking  is  laid  on  one 
side  of  the  pit  on  the  ground,  and  the  clay  thrown  upon  this,  the  different 
grades  being  kept  separate. 

When  the  clay  lies  above  the  ground-  or  road-level  there  is  less  trouble 
with  water,  and  it  is  not  necessary  to  work  the  clay  in  pits,  although  the 
general  system  of  working  forward  in  a  succession  of  pit-like  excavations 


Sandy  clay 

Stoneware  clay 
Pipe  clay 


FIG.  41. — Section  of  pit  working  in  Middlesex  district.     (After  Ries,  N.  J.  Geol. 
Surv.,  Fin.  Kept.,  VI,  p.  33,  1904.) 

or  recesses  is  followed.  In  such  banks  the  cart  or  car  is  backed  against 
the  face  of  the  excavation  and  the  clay  thrown  into  it. 

Unless  a  number  of  pits  are  being  dug  at  the  same  time,  the  output 
of  any  one  deposit  or  of  any  one  grade  is  necessarily  small,  since  five 
or  six  different  kinds  are  sometimes  obtained  from  one  pit.  It  would 
also  seem  that  by  this  method  any  one  grade  of  clay  might  show  greater 
variation  than  if  the  excavations  were  more  extended,  for  the  reason  that 
since  clay-beds  are  liable  to  horizontal  variation,  the  material  extracted 
from  one  pit  might  be  different  from  that  taken  from  another  farther  on. 
Against  this  we  may  of  course  argue  that  the  clays  from  different  pits 
get  mixed  up  on  the  storage  pile. 

As  these  pits  are  small  and  the  time  required  for  sinking  one,  namely, 
two  or  three  days,  is  not  very  great,  but  little  water  runs  in  them,  although 
in  some  much  water  comes  from  sand  or  other  layers  it  at  are  sometimes 
inter-stratified  with  the  clay.  The  surface  drainage  is  commonly  diverted 
by  means  of  ditches  dug  around  the  top  of  the  pit.  In  some  districts 


PLATE   IX 


FIG.  1. — Digging  clay  by  means  of  open  pits.  At  the  top  of  the  bank,  in  the  back- 
ground, a  workman  is  driving  a  wedge  into  the  clay  in  order  to  break  it  off. 
The  clay  is  hauled  to  the  yards  in  carts.  (After  Ries,  N.  J.  Geol.  Surv.,  Fin. 
Kept.,  VI,  p.  35,  1904.) 


FIG.  2. — Removing  the  overburden  from  a  shale-bed   by  hydraulicking. 
Photo  loaned  by  Illinois  Geological  Survey.) 

207 


KINDS  OF  CLAYS  209 

there  is  a  bed  of  water-bearing  sand  underlying  the  lowest  clay  dug,  and, 
as  this  is  approached,  hand-pumps  have  to  be  used  to  keep  down  the 
water  until  the  last  spit  of  clay  is  all  taken  out. 

In  digging  a  pit  of  clay,  it  is  well  to  avoid  discarding  a  clay  of  lower 
grade  or  mixing  it  with  the  dirt  stripping,  because  it  has  no  market 
value  at  the  time.  Careless  handling  of  the  medium-grade  clays  in  the 
Woodbridge  and  Perth  Amboy  districts  in  the  early  days  of  their  develop- 
ment has  been  the  means  of  spoiling  much  clay  that  would  now  be 
salable. 

Haulage. — If  the  distance  from  the  bank  to  works  or  shipping-point 
is  short,  wheelbarrows  or  one-horse  carts  are  used,  but,  if  a  longer  haulage 
is  necessary,  it  is  more  economical  to  lay  light  tracks  and  haul  the  clay 
In  cars  drawn  by  horses  or  small  engines.  Steam  haulage  is  economical 
for  a  distance  of  perhaps  not  less  than  1000  feet,  and  provided  the 
locomotive  is  kept  constantly  employed. 

When  a  pit  is  to  be  opened,  the  top  dirt,  stripping  or  bearing,  as  it 
Is  variously  called,  is  first  removed  to  some  place  where  it  will  not  have 
to  be  disturbed,  in  order  to  avoid  the  cost  of  a  second  moving,  but,  after 
one  pit  has  been  started,  it  is  often  customary  to  use  the  stripping  from 
a  new  pit  for  filling  the  old  one. 

The  cost  of  removing  the  stripping  will  depend  on  its  character, 
whether  hard  or  soft,  the  distance  to  be  moved,  and  the  possibility 
of  its  being  used  for  any  purpose,  such  as  filling  or  grading.  The  methods 
of  removal  employed  will  also  affect  the  expense.  If  the  thickness  of 
the  overburden  is  considerable  and  a  large  quantity  has  to  be  removed, 
it  is  cheaper  to  dig  it  with  a  steam-shovel  than  by  hand.  Wheel-scrapers 
are  also  employed  at  times,  and  if  the  distance  to  the  dump-heap  is  short 
the  material  can  be  carried  there  in  the  scraper.  If  the  stripping  can  be 
used  to  mix  with  the  clay  it  is  sometimes  dug  with  shovels  and  screened 
to  free  it  from  pebbles.  A  method  tried  at  some  localities  is  to  remove 
the  sandy  or  gravelly  overburden  by  washing  (PI.  IX,  Fig.  2).  This 
Is  done  by  directing  a  powerful  stream  of  water  from  a  hose  against 
the  face  or  surface  of  the  gravel  and  washing  it  down  into  some  ditch 
along  which  it  runs  off. 

In  selecting  the  site  for  a  dump-heap,  care  should  be  taken  not  to 
locate  it  over  any  clay -deposit  which  is  to  be  worked  out  later,  but  the 
presence  or  absence  of  such  clay  under  the  proposed  dump  can  commonly 
be  determined  by  a  few  bore-holes  made  with  an  auger. 

Kaolin-mining. — Since  most  of  the  kaolin-deposits  worked  in  the 
United  States  are  long  and  narrow,  a  method  often  adopted  consists  in 
sinking  a  circular  pit  in  the  kaolin  about  25  feet  in  diameter.  As  the 


210  CLAYS 

pit  proceeds  in  depth  it  is  lined  with  a  cribwork  of  wood  (PI.  XXXIV, 
Fig.  1).  This  lining  is  extended  to  the  full  depth  of  the  pit,  which 
varies  from  50  to  100  or  even  120  feet.  When  the  bottom  of  the  kaolin 
has  been  reached  the  filling-in  of  the  pit  is  begun,  the  cribwork  being 
removed  from  the  bottom  upwards  as  the  filling  proceeds.  If  there  is 
any  overburden  it  is  used  for  filling  up  the  old  pits.  The  kaolin  is  removed 
from  the  pit  with  a  bucket-hoist,  and  as  soon  as  one  pit  is  filled  a  new 
one  may  be  sunk  in  the  same  manner  right  next  to  it.  In  this  way  the 
whole  vein  is  worked  out,  and,  if  the  deposit  is  large,  several  pits  may 
be  sunk  at  the  same  time. 

A  somewhat  unique  method  of  mining  is  that  practiced  in  the  Corn- 
wall, Eng.,  district  where  the  material  to  be  mined  is  a  sandy  kaolin  of 
great  depth.  The  method  of  working  is  described  by  J.  H.  Collins1 
as  follows: 

"The  depth  of  the  overburden  and  the  extent  of  the  workable  clay-ground 
having  been  sufficiently  ascertained  by  pitting  or  boring  (often  by  a  combination 
of  both  methods),  a  shaft  is  sunk  in  the  firm  rock,  near  the  clay  which  is  to  be  worked, 
and  to  a  depth  of  15  or  20  fathoms.  A  cross-cut  is  put  out  from  the  bottom  of 
the  shaft  into  the  clay-ground.  This  must  be  securely  timbered  where  it  approaches 
the  clay-ground.  The  overburden  having  been  removed  arid  deposited  at  a  con- 
venient spot,  a  raise  is  put  up  vertically  through  the  clay  to  the  surface.  In  this 
is  placed  (vertically)  a  wooden  launder,  which  reaches  within  a  fathom  or  two  of 
the  surface,  and  is  provided  with  lateral  openings  a  foot  or  two  apart,  each  of  which 
is  closed  by  a  temporary  wooden  cover.  This  is  called  a  'buttonhole'  launder. 
The  shaft  having  been  equipped  with  a  suitable  pump,  work  may  be  begun  at  once. 
The  clay-ground,  to  a  depth  of  a  fathom  or  so  around  the  buttonhole  launder,  is 
removed  and  a  stream  of  water,  pumped  from  the  shaft  or  brought  along  from 
some  other  source,  is  made  to  flow  over  the  broken  ground,  which  is  at  the  same 
time  stirred  up  as  may  be  necessary.  The  fine  clay  particles,  held  in  suspension 
in  the  milky  stream,  pass  down  the  launder  and  along  the  cross-cut  to  the  shaft, 
whence  they  are  pumped  up  for  further  treatment.  The  quartz-grains  ('sand') 
and  the  coarser  particles  of  mica,  schorl  (tourmaline),  etc.,  are  shoveled  up  from 
around  the  launder  and  trammed  away  to  the  waste-dump.  As  the  depth  of  the 
workings  increases,  other  'buttonholes'  are  opened,  the  inclination  of  the  clay 
'stopes'  being  at  the  same  time  maintained  by  removing  more  overburden  and 
by  cutting  away  the  margin  of  the  pit. 

"The  clay  raised  in  suspension  from  the  shaft  by  the  pump  is  made  to  flcvr 
through  a  long  series  of  shallow  troughs  called  '  micas ';  these  are  set  nearly  level,  and 
the  stream  is  divided  again  and  again  so  as  to  lessen  the  rate  of  flow  and  to  allow 
the  fine  sandy  and  micaceous  particles  to  settle.  Finally,  the  refined-clay  stream 
is  led  into  circular  stone-lined  pits,  preferably  from  12  to  18  ft.  deep,  where  the 
clay  settles  to  a  creamy  consistency,  while  the  overflow  of  nearly  clear  water 
is  conducted  back  to  the  clay-stop 3s,  where  it  again  serves  for  the  washing  pro- 
cess. The  deposit  in  the  'micas'  is  swept  out  from  time  to  time,  an  operation  which 

1  Min.  Indus.,  XIII,  p.  472,   1905. 


KINDS  OF  CLAYS  211 

occupies  only  a  few  minutes,  after  which  they  are  again  ready  to  receive  the  clay 
stream.  The  thickened  clay  from  the  pits  passes  to  large  stone-built  or  stone- 
lined  tanks,  which  are  from  5  to  8  ft.  deep.  In  many  cases  they  consist  merely 
of  two  dry-built  rubble  walls  placed  as  far  rpart  as  the  depth  of  the  tank  and 
puddled  between  with  waste  sand,  containing  a  little  clay  from  some  previous 
working.  From  the  tanks,  after  further  settlement,  it  is  trammed  into  the  kiln 
or  'dry.'  The  deposit  in  the  micas  is  sometimes  re-washed,  so  as  to  yield  an 
inferior  product,  which  is  commercially  sold  as  'mica'  or  'mica-clay.' 

"Carclazite1  varies  much  in  productiveness;  in  obtaining  one  ton  of  fine  clay 
the  following  by-products  have  to  be  dealt  with :  From  3  to  7  tons  of  sand,  average 
4  tons;  2  to  5  cwt.  of  coarse  mica,  average  3  cwt.;  1  to  3  cwt.  of  fine  mica  (mica 
clay),  average  2  cwt.;  £•  to  1  cwt.  of  stones,  mostly  quartz,  with,  generally,  much 
'schorl'  from  the  stony  veins  or  branches.  A  cubic  fathom  of  carclazite  of  good 
quality  will  yield  about  three  tons  of  fine  clay;  on  an  average  nearly  half  a  cubic 
fathom  of  overburden  must  be  removed  in  order  to  get  it." 


A  somewhat  similar  method  has  recently  been  adopted  to  work  the 
kaolin-deposits2  at  West  Cornwall,  Conn.,  and  the  following  description 
of  it  is  given  by  A.  R.  Ledoux : 2 

"The  kaolin-deposit  of  West  Cornwall  is  an  alteration  in  situ — that  is,  it  is  not 
sedimentary.  A  series  of  clay-veins,  dipping  about  50°  from  the  vertical,  lie  between 
a  foot-wall  of  limonite  and  a  hanging-wall  of  gneiss  and  hornblende  schist.  The 
clay-veins  alternate  with  veins  or  seams  of  more  or  less  broken  quartz  and  unaltered 
feldspar.  The  deposit,  which  occurs  at  a  point  about  600  ft.  above  the  Housatonic 
River,  was  opened  five  years  ago,  and  about  5000  tons  of  washed  kaolin  has  been 
extracted  from  open  pits  and  sold. 

"Mr.  Wanner  conceived  the  scheme  to  disintegrate  the  kaolin  in  situ  by  means 
of  jets  of  water  under  sufficient  pressure,  and  floating  the  resultant  product  to  the 
surface.  To  accomplish  this  result  holes  are  drilled  through  the  overlying  gneiss, 
a  pipe  of  4-in.  internal  diameter  is  inserted  into  the  bore  and  driven  into  the  clay- 
body  to  within  a  few  feet  of  the  foot-wall.  The  wells  in  operation  are  from  50  to 
198  ft.  deep.  Into  this  4-in.  pipe  or  'casing  '  an  interior  pipe  is  inserted  of  2-in. 
external  diameter,  leaving  an  annular  space  of  1  in.  for  the  flow  of  the  slip.  The 
lower  end  of  the  internal  pipe  is  provided  with  a  mouthpiece  with  several  nozzle- 
like  openings  for  the  exit  of  the  water;  the  mouthpiece  rests  on  the  clay-body,  and 
the  interior  pipe  sinks  gradually  as  the  clay  is  removed  until  it  rests  on  the  foot- 
wall  of  the  vein.  For  the  operation  of  these  'hydraulics'  a  head  of  water  equivalent 
to  a  pressure  of  from  40  to  60  Ibs.  per  sq.  in.  is  required,  according  to  the  nature  of 
the  vein-matter. 

"Residual  kaolin  slacks  more  or  less  readily,  according  to  the  amount  of  sand 
and  mica  mixed  with  it.  In  the  case  in  point,  it  has  been  found  that  a  pressure  of 
40  Ibs.  is  amply  sufficient  to  cause  the  disintegration,  the  vein-matter  contains 
20  per  cent  and  the  slip,  discharged  by  the  hydraulics,  from  60  to  75  per  cent  of 
pure  kaolin.  The  purity  of  the  discharged  slip  is  inversely  proportional  to  the  veloc- 
ity of  the  overflow. 

1  A  name  applied  to  the  kaolin. 

2  Amer.  Inst.  Min.  Eng.,  Bi-monthly  Bull.,  No.  9,  p.  379,  1906. 


212  CLAYS 

"Observations  made  during  the  1905  season's  work  have  shown  that  the 
overflow  contains  from  5  to  10  per  cent  of  solid  matter.  A  discharge  of  100  gaL 
per  min.  through  the  annular  space  of  9.42  sq.  in.  from  a  depth  of  127  ft.  yielded 
5  per  cent  of  solid  matter,  of  which  75  per  cent  was  pure  kaolin,  while  a  discharge 
of  200  gal.  per  min.,  through  the  same  orifice  from  the  same  depth,  gave  a  slip  con- 
taining 10  per  cent  of  solid  matter  but  only  54  per  cent  of  pure  kaolin,  the  rest 
being  finely  divided  quartz  and  mica. 

"In  addition  to  the  lessening  of  the  cost  of  extraction,  the  method  described 
has  effectually  solved  the  transportation  of  the  product  to  the  railroad.  Hereto. 
fore,  the  kaolin  washed  and  dried  at  the  mines  was  carted  by  teams  over  a  difficult 
mountain  road  to  West  Cornwall,  4  miles  distant.  The  fuel  for  the  whole  plant  had 
to  be  hauled  up  the  mountain  the  same  distance.  With  slip  issuing  from  the 
hydraulics  of  only  10  per  cent  of  solid  matter  and  sufficient  fineness  to  pass  through 
100-mesh  screens,  the  conveyance  of  the  product  through  a  pipe-line  to  the  Housa- 
tonic  Valley  offers  no  difficulty,  and  the  company  now  contemplates  the  erection 
of  a  new  washing-plant  adjacent  to  the  river  and  railroad." 

Underground  workings.— This  method  may  be  resorted  to  when 
the  clay-bed  is  covered  by  such  a  great  thickness  of  overburden  that 
its  removal  would  be  too  costly.  If  the  bed  sought  outcrops  on  the  side 
of  a  hill,  a  tunnel  or  drift  is  driven  in  along  the  clay-bed,  as  shown  in 
PI.  VII,  Fig.  2,  but  in  case  no  outcrop  is  accessible  it  is  necessary  to 
sink  a  vertical  shaft  (Fig.  53)  until  the  bed  of  clay  is  reached,  and  from 
this,  levels  or  tunnels  may  be  driven  along  the  clay-bed. 

Underground  methods  are  desirable,  however,  only  under  certain 
conditions,  which  may  be  enumerated  herewith: 

1.  In  the  case  of  high-grade  clays. 

2.  Where  there  is  much  overburden  as  compared  with  the  thickness 
of  the  clay-deposit. 

3.  There  should,  if  possible,  be  a  solid  dense  layer  overlying  the  clay 
stratum,  otherwise  the  expense  of  timbering  for  supporting  the  roof 
may  be  too  great.     Timbering  is  nearly  always  necessary  in  underground 
clay-work.     Where  the  clay  is  not  inter-stratified  between  dense  water- 
tight beds,  it  is  often  necessary  to  leave  the  upper  and  lower  foot  of 
clay  to  form  a  roof  and  floor. 

4.  The  workings  should  be  free  from  water,  both  on  account  of  the 
cost  of  removing  the  same  and  because  of  the  tendency  of  wet  ground 
to  slide. 

5.  The  output  is  usually  restricted,  unless  the  workings  underlie  a. 
large  area,  and  can  be  worked  by  several  shafts  or  drifts. 

Soft  clays  are  rarely  worked  by  underground  methods,  but  in  Mary- 
land, Indiana,  Missouri,  Pennsylvania,  and  a  few  other  localities,  the 
shaly  clays  associated  with  the  coals  are  frequently  mined  by  shafts, 
drifts,  or  slopes. 


KINDS  OF  CLAYS  213  " 

Some  of  the  mines  are  lighted  by  electricity  and  also  equipped  with 
electric  hoists,  drills,  and  haulage. 

Preparation  of  Clay  for  Market 

Unless  clay  is  to  be  used  for  higher  grades  of  ware,  it  rarely  requires 
much  preparation  to  make  it  marketable,  for,  since  the  impurities  in 
clay  often  run  in  streaks  or  beds,  they  can  be  avoided  in  mining.  Large 
concretions,  pyrite  nodules,  and  lumps  of  lignite  are  often  picked  out  by 
hand  and  thrown  to  one  side.  Where  the  impurities  are  present  in  a 
finely  divided  form  and  distributed  throughout  the  clay,  screening  or 
hand-picking  may  be  ineffective,  and  washing  is  necessary. 

Washing. — The  method  of  washing  most  commonly  adopted  is  the 
troughing  method,  in  which  the  clay,  after  being  stirred  up  and  disinte- 
grated with  water,  is  washed  into  a  long  trough  along  which  it  passes, 
dropping  its  sandy  impurities  on  the  way  and  finally  reaching  the  set- 
tling-vats, into  which  the  clay  and  water  are  discharged,  and  where  the 
clay  finally  settles. 

Details. — The  disintegration  of  the  clay  is  generally  accomplished  in 
washing-troughs.  These  consist  of  cylindrical  or  rectangular  troughs, 
in  which  there  revolves  a  shaft,  bearing  a  series  of  arms  or  stirrers.  The 
clay  may  be  taken  from  the  bank  direct  to  the  washer,  or  it  may  first 
receive  a  soaking  in  a  pit  to  slake  it.  As  the  clay  is  put  into  the  washer 
a  stream  of  water  is  directed  on  it,  and  the  revolving  blades  break  up  the 
clay  so  that  it  goes  more  readily  into  suspension.  The  water,  with 
suspended  clay,  then  passes  out  at  the  opposite  end  from  which  the  water 
entered. 

The  troughing  (PI.  X,  Fig.  1)  into  which  the  material  is  discharged 
is  constructed  of  planking  and  has  a  rectangular  cross-section.  Its 
slope  is  very  gentle,  not  more  than  1  inch  in  20  feet  usually,  and  its 
total  length  may  be  from  500  to  700  feet,  or  even  1000  feet.  In  order  to 
economize  space  it  is  usually  built  in  short  lengths,  which  are  set  side 
by  side,  and  thus  the  water  and  clay  follow  a  zigzag  course.  The  pitch, 
width,  and  depth  of  the  troughing  may  be  varied  to  suit  the  conditions, 
for  at  some  localities  it  is  necessary  to  remove  more  sand  than  at  others. 
If  the  clay  contains  very  much  fine  sand  the  pitch  must  be  less  than  if 
the  sand  is  coarse,  since  fine  sand  will  not  settle  in  a  fast  current.  In 
the  case  of  very  sandy  clays,  it  is  customary  to  place  sand-wheels  at  the 
upper  end  of  the  troughing.  These  are  wooden  wheels  bearing  a  number 
of  iron  scoops  on  their  periphery.  As  the  wheel  revolves  the  scoops 
pick  up  the  coarse  sand  which  has  settled  in  the  trough  and,  as  the 


214  CLAYS 

scoop  reaches  the  upper  limit  of  its  turn  on  the  wheel,  by  its  inverted 
position  it  drops  the  sand  upon  a  slanting  chute,  which  carries  it  outside 
the  trough. 

By  the  time  the  water  reaches  the  end  of  the  troughing  nearly  all 
the  sand  has  been  dropped  and  the  water  and  clay  are  discharged  into 
the  settling-tanks,  passing  first,  however,  through  a  screen  of  about  80 
or  100  mesh.  This  catches  any  particles  of  dirt  or  twigs  and  thus  keeps 
the  clay  as  clean  as  possible. 

The  settling-tanks  (PL  X,  Fig.  1)  are  of  wood,  usually  about  4  feet 
deep,  8  feet  wide,  and  40  or  50  feet  long.  As  soon  as  one  is  filled  the  water 
and  clay  are  diverted  into  another.  When  the  clay  has  settled,  most  of 
the  clear  water  is  drawn  off,  and  the  cream-like  mass  of  clay  and  water 
in  the  bottom  of  the  vat  is  drawn  off  by  means  of  slip-pumps  and  forced 
into  the  presses  (PI.  X,  Fig.  2).  These  consist  of  flat  iron  or  wooden 
frames,  between  which  are  flat  canvas  bags.  The  latter  are  either  con- 
nected by  nipples  with  the  supply-tubes,  or  else  there  may  be  a  central 
opening  in  all  the  press  bags  and  frames,  which,  being  in  line,  form  a 
central  tube  when  the  press  is  closed  up.  By  means  of  pressure  from 
the  pumps,  the  slip  is  then  forced  into  the  press,  and  the  water  is  also 
driven  out  of  it.  When  the  water  has  been  squeezed  out  the  press  is 
opened,  and  the  sheets  of  clay  are  removed  from  the  press  cloths  and 
sent  to  the  drying-room  or  racks. 

Washing  is  applied  chiefly  to  kaolins,  but  is  carried  out  to  a  less  extent 
on  fire-clays,  glass-pot  clays,  and  ball-clays. 

Air  separation. — This  is  a  method  of  cleansing  clays  which  has  been 
rarely  tried,  yet,  in  some  of  the  cases  where  it  has  been  used,  is  said  to 
have  met  with  success.  It  is  especially  applicable  to  those  clays  from 
which  it  is  necessary  to  remove  simply  coarse  or  sandy  particles.  The 
process  consists,  in  brief,  in  feeding  the  dry  clay  into  a  pulverizer,  which 
reduces  it  to  the  condition  of  a  very  fine  powder.  As  the  material  is 
discharged  from  the  pulverizer  into  a  long  box  or  tunnel,  it  is  seized  by 
a  powerful  current  of  air,  which  at  once  picks  up  the  fine  particles  and 
carries  them  along  to  the  end  of  the  airway,  where  they  are  dropped  into 
a  bin.  The  coarser  particles,  which  are  too  heavy  to  be  picked  up  by 
the  current,  drop  back  and  are  carried  through  the  pulverizer  once  more. 
Such  a  method  would  be  especially  applicable  to  kaolins  that  are  free 
from  iron,  but  probably  would  not  be  found  adaptable  to  many  of  those 
containing  ferruginous  particles. 

There  are  several  forms  of  separators  on  the  market.  In  the  Ray- 
mond pulverizer  and  separator  the  material  is  pulverized  in  the  lower 
part  of  the  machine  and  then  thrown  upward,  the  finer  particles  being 


PLATE   X 


FIG.  1. — View  showing  portion  of  sand-troughs,  settling-tanks,  and  drying-racks 
at  a  kaolin-washing  plant.     (After  Ries,  Md.  Geol.  Surv.,  IV,  p.  270,  1902.) 


j?IG  2. — Filter-press  for  removing  water  from  washed  or  blunged  clays.  The 
portion  at  the  left  end  has  been  emptied  and  the  leaves  of  clay  taken  from  it 
are  on  the  car.  The  workman  is  just  removing  a  leaf  of  clay  from  the  press. 
(After  Ries,  N.  Y.  State  Mus.,  Bull.  35,  p.  792,  1900.) 

215 


KINDS  OF  CLAYS  217 

earned  off  by  a  fan  to  the  discharge-hopper,  the  coarser  ones  falling 
back  into  the  hopper. 

THE    MANUFACTURE    OF   CLAY    PRODUCTS 

Uses  of  Clay 

Probably  few  persons  have  any  conception  of  the  many  different 
applications  of  clay  in  either  its  raw  or  burned  condition.  These  varied 
uses  can  be  best  shown  by  the  following  table,  compiled  originally  by 
R.  T.  Hill 1  and  amplified  by  the  writer: 

Domestic. —  Porcelain,  white  ware,  stoneware,  yellow  ware,  and 
Rockingham  ware  for  table  service  and  for  cooking;  majolica  stoves; 
polishing-brick,  Bath  brick,  fire-kindlers. 

Structural. — Brick;  common,  front,  pressed,  ornamental,  hollow, 
glazed,  adobe;  terra-cotta;  roofing-tile;  glazed  and  encaustic  tile;  drain- 
tile;  paving-brick;  chimney-flues;  chimney-pots;  door-knobs;  fireproofing; 
terra-cotta  lumber;  copings;  fence-posts. 

Refractories. — Crucibles 'and  other  assaying  apparatus;  gas-retorts; 
fire-bricks;  glass  pots  and  blocks,  for  tank-furnaces;  saggers;  stove  and 
furnace  bricks;  blocks  for  fire-boxes;  tuyeres;  cupola  bricks;  mold  linings 
for  steel  castings. 

Engineering. — Puddle;  Portland  cement;  railroad  ballast;  water 
conduits;  turbine-wheels;  electrical  conduits;  road  metal. 

Hygienic. — Urinals,  closet  bowls,  sinks,  washtubs,  bathtubs,  pitchers, 
sewer-pipe,  ventilating-flues,  foundation-blocks,  vitrified  bricks. 

Decorative.  —  Ornamental  pottery,  terra-cotta,  majolica,  garden- 
stands,  tombstones. 

Minor  uses. — Food  adulterant;  paint  fillers;  paper  filling;  electric 
insulators;  pumps;  fulling  cloth;  scouring-soap ;  packing  for  horses' 
feet;  chemical  apparatus;  condensing-worms;  ink-bottles;  ultramarine 
manufacture;  emery-wheels;  play  ing-marbles;  battery-cups;  pins,  stilts 
and  spurs  for  potters'  use;  shuttle-eyes  and  thread -guides;  smoking-pipes; 
umbrella-stands;  pedestals;  filter-tubes;  caster-wheels;  pump-wheels; 
electrical  porcelain;  foot-rules;  plaster;  alum. 

METHODS    OF   MANUFACTURE 

In  the  following  pages  it  is  intended  to  give  a  brief  account  of  the 
methods  of  manufacture  employed,  so  as  to  enable  one  to  see  what 
requirements  a  clay  has  to  meet.  The  more  important  products  are 

1  Mineral  Resources,  U.  S.,  1891,  p.  475,  Washington. 


218  CLAYS 

taken  up  in  the  following  order:  Building-  and  paving-brick;  sewer- 
pipe;  drain-tile;  hollow  ware;  conduits;  fire-brick;  roofing- tile;  terra- 
cotta; floor-  and  wall-tile;  pottery. 

Building-brick  and  Paving-brick 

Building-brick  include  common  brick,  face  and  pressed  brick,  enamel 
brick,  and  glazed  brick,  while  paving-brick  form  a  class  by  themselves. 

Common  brick  include  all  those  used  for  ordinary  structural  work, 
and  are  employed  usually  for  side  and  rear  walls  of  buildings,  or,  indeed, 
for  any  portion  of  the  structure  where  appearance  is  of  minor  importance, 
although  for  the  sake  of  economy  they  are  sometimes  used  for  front 
walls.  They  are  often  made  without  much  regard  to  color,  smoothness 
of  surface,  or  sharpness  of  edges. 

Face,  front,  or  pressed  brick  include  those  made  with  greater  care, 
and  usually  from  a  better  grade  of  clay,  much  consideration  being  given 
to  their  uniformity  of  color,  even  surface,  and  straightness  of  outline. 
Red  ones  were  formerly  in  great  demand,  but  at  the  present  time  buff, 
white,  and  buff  with  manganese  speckles  are  the  most  sought. 

Enamel  brick  are  those  which  have  a  coating  of  enamel  on  one  or 
sometimes  two  sides.  The  body  is  usually  a  fire-clay. 

Glazed  brick  differ  from  enamel  brick  in  being  coated  with  a  trans- 
parent glaze  instead  of  an  opaque  enamel.  They  are  used  more  in  Europe 
than  in  the  United  States. 

The  clays  used  for  brickmaking  have  already  been  described  (p.  185). 

Manufacture  of  Brick 

The  methods  employed  in  the  manufacture  of  common  and  pressed 
brick  are  usually  very  similar,  the  differences  lying  chiefly  in  the  selection 
of  material,  the  degree  of  preparation,  and  the  amount  of  care  taken  in 
burning.  The  manufacture  of  bricks  may  be  separated  into  the  following 
steps:  preparation,  molding,  drying,  and  burning. 

Preparation 

In  brickmaking  some  preparation  of  the  clay  is  commonly  necessary, 
since  few  clays  can  be  sent  direct  from  the  bank  to  the  molding-machine, 
although  some  common-brick  manufacturers  reduce  the  preparation 
process  to  a  minimum. 

Many  clays  are  prepared  by  weathering,  especially  if  they  are  to  be 


KINDS  OF  CLAYS  219 

used  in  the  manufacture  of  pressed  brick.  This  is  done  by  distributing 
the  clay  over  some  flat  surface  in  a  thin  layer  not  more  than  2  or  3  feet 
in  thickness  and  allowing  it  to  lie  there  exposed  to  frost,  rain,  wind,  and 
sun,  which  results  in  a  slow  but  thorough  disintegration  or  slacking. 
Iron  nodules,  if  present,  tend  to  rust,  and  are  thus  more  easily  seen  and 
rejected,  while  pyrite,  if  present,  may  also  decompose  and  give  rise  to 
soluble  compounds,  which  form  a  white  crust  on  the  surface  of  the  clay. 
Although  some  clays  are  prepared  by  weathering,  yet  in  great  part  their 
disintegration  is  done  by  artificial  means. 

Crushers. — When  the  clay  or  shale  is  to  be  disintegrated  or  crushed,, 
it  is  commonly  done  dry,  and  the  machine  employed  varies  with  the 
character  of  the  material.  Hard  shale  is  often  disintegrated  in  a  jaw- 
crusher,  which  consists  of  two  movable  jaws  that  interact  and  are  set 
closer  together  at  their  lower  than  at  their  upper  ends. 

Dry  pans. — Where  a  soft  shale  or  a  hard,  tough,  dry  clay  is  to  be  used,, 
dry  pans  (PI.  XI,  Fig.  1)  are  frequently  employed.  These  consist  of  a. 
circular  pan  in  which  there  revolve  two  iron  wheels  on  a  horizontal 
axis.  The  wheels  turn  because  of  the  friction  against  the  bottom  of  the 
pan,  the  latter  being  rotated  by  steam-power,  and  in  turning  they  grind 
by  reason  of  their  weight,  which  ranges  from  2000  to  5000  pounds. 
The  bottom  of  the  pan  is  made  of  removable  perforated  plates,  so  that 
the  material  falls  through  as  soon  as  it  is  ground  fine  enough.  Two 
scrapers  are  placed  in  front  of  the  rollers  to  throw  the  material  in  their 
path. 

Disintegrators,  which  are  sometimes  used  for  breaking  up  clay  or 
shale,  consist  of  several  drums,  or  knives  on  axles,  revolving  rapidly 
within  a  case  and  in  opposite  directions.  As  the  lumps  of  clay  are 
dropped  into  the  machine  they  are  thrown  violently  about  between 
the  drums  and  also  strike  against  each  other,  thus  pulverizing  the  material' 
completely  and  rapidly.  Their  capacity  is  large,  but  much  power  is  also 
required  to  drive  them. 

Rolls. — These  are  often  employed  for  breaking  up  clay  and  pebbles,, 
and  where  dry  material  is  used  they  are  quite  effective;  but  if  damp 
clay  is  put  through  them,  as  is  done  at  some  yards,  the  lumps  are  simply- 
flattened  out.  The  surface  of  the  rolls  is  smooth,  corrugated  or  toothed,, 
or  tapering,  and  the  two  rolls  revolve  in  opposite  directions  and  with 
differential  velocities  of  from  500  to  700  revolutions  per  minute.  In 
some  the  stones  in  the  clay  are  crushed,  in  others  they  are  thrown 
out,  by  reason  of  the  construction  of  the  machine. 

All  the  machines  mentioned  above  are  used  on  dry  or  nearly  dry 
clay,  but  there  are  several  other  types  which  are  employed  for  wet  clays 


220  CLAYS 

only,  and  these  in  addition  to  breaking  up  the  clay  may  also  be  used 
to  mix  it.  The  process  is  sometimes  termed  tempering. 

Soak-pits. — Soak-pits,  used  at  many  small  yards  for  preparing  the 
clay,  are  simply  pits  in  which  the  clay,  with  water  added,  is  allowed  to 
soak  overnight. 

Ring-pits. — Ring-pits  (PL  XI,  Fig.  2),  employed  at  many  common- 
brick  yards,  are  circular  pits  from  20  to  25  feet  in  diameter,  about  3  feet 
deep,  and  lined  with  boards  or  brick.  Revolving  in  this  pit  is  an  iron 
wheel,  6  feet  in  diameter,  so  geared  as  to  travel  around  the  pit  in  a  spiral 
path,  thus  thoroughly  mixing  the  mass.  The  tempering  is  accomplished 
usually  in  5  or  6  hours,  and  one  pit  commonly  holds  enough  clay  for 
from  25,000  to  30,000  brick.  Ring-pits  are  cheaper  than  pug-mills,  but 
have  a  lower  capacity  and  require  more  room.  They  are  operated  by 
either  steam-  or  horse-power. 

Pug-mills  (Fig.  42)  are  semi-cylindrical  troughs,  varying  in  length 
from  3  to  14  feet,  with  6  feet  as  a  fair  average.  In.  this  trough  there 
revolves  a  horizontal  shaft,  bearing  knives  set  spirally  around  it  and 
having  a  variable  pitch.  The  clay  and  water  are  charged  at  one  end, 
and  the  blades  on  the  shaft  not  only  cut  up  the  clay  lumps,  but  mix  the 
mass,  at  the  same  time  pushing  it  towards  the  discharge  end. 

Pug-mills  are  thorough  and  continuous  in  their  action,  take  up  less 
space  than  ring-pits,  and  do  not  require  much  power  to  operate.  They 
are  used  in  connection  with  both  stiff-mud  and  soft-mud  machines. 

Wet  pans  (PL  XII,  Fig.  1). — These  are  similar  to  dry  pans,  but 
differ  from  them  in  having  a  solid  bottom.  The  material  and  water 
are  put  into  the  pan,  and  the  clay  is  crushed  and  tempered  at  the  same 
time.  Where  the  clay  contains  hard  lumps  of  limonite  or  pyrite  nodules, 
a  wet  pan  is  superior  to  a  pug-mill  or  disintegrator,  for  the  charge  is 
crushed  and  tempered  in  a  few  minutes,  and  can  then  be  replaced  by 
another  one. 


Molding 

Bricks  are  molded  by  one  of  four  methods,  namely,  soft-mud,  stiff- 
mud,  dry-press,  and  semi-dry-press,  although  in  reality  there  is  not 
much  difference  between  the  last  two. 

Soft-mud  process. — In  this  method  the  clay,  or  clay  and  sand,  are 
mixed  with  water  to  the  consistency  of  a  soft  mud  or  paste  and  pressed 
into  wooden  molds.  Since,  however,  the  wet  clay  is  sticky  and  likely 
to  adhere  to  a  wooden  surface,  the  molds  are  sanded  each  time  before 
being  filled.  Soft-mud  bricks,  therefore,  show  five  sanded  surfaces, 


PLATE   XI 


FIG.  1. — Dry  pan  used  for  grinding  hard  clays,  shale,  and  brick.     (After  H.  Ries, 
N.  Y.  State  Museum,  Bull.  35,  p.  765,  1600.) 


FIG.  2. — Ring-pit  for  mixing  clays.     (After  H.  Ries,  N.  Y.  State  Museum,  Bull.  35, 

p.  659,  1900.) 

221 


OF  THf 

UNIVERSITY 

OF 


PLATE   Xli 


FIG.    1. — Wet   pan   for   grinding   and   mixing   clays   or   shales.      (After   H.   Ries, 
Md.  Geol.,  IV,  p.  356,  1902.) 


FIG.  2.— Cutting-table  of  stiff-mud  brick-machine.     (After  H.  Ries,  N.  Y.  State 
Mus.,  Bull.  35,  p.  662,  1900.) 

225 


or  THF 
f    UNIVERSITY   ] 

OF 


KINDS  OF  CLAYS 


227 


and  the  sixth  surface  will  be  somewhat  rough,  due  to  the  excess  of  clay 
being  wiped  off  even  with  the  top  of  the  mold. 

Soft-mud  bricks  are  molded  either  by  hand  or  in  machines. 

The  soft-mud  machine  (Fig.  43)  consists  usually  of  an  upright  box 
of  wood  or  iron,  in  which  there  revolves  a  vertical  shaft  bearing  several 
blades  or  arms.  Attached  to  the  bottom  of  the  shaft  is  a  curved  arm 
which  forces  the  clay  into  the  press-box.  The  molds,  after  being  sanded, 
are  shoved  underneath  the  press-box  from  the  rear  side  of  the  machine. 
Each  mold  has  six  divisions,  and  as  it  comes  under  the  press-box  the 


FIG.  43.— A  soft-mud  brick-machine. 

plunger  descends  and  forces  the  soft  clay  into  it.  The  filled  mold  is 
then  pushed  forward  automatically  upon  the  delivery-table,  while  an 
empty  one  moves  into  its  place.  As  soon  as  the  mold  is  delivered  its 
upper  surface  is  " struck"  off  by  means  of  an  iron  scraper.  Under 
favorable  conditions  soft-mud  machines  have  a  capacity  of  about  40,000 
brick  per  day  of  ten  hours,  although  they  rarely  attain  this. 

The  soft-mud  process  was  the  first  method  of  molding  employed, 
and  is  still  largely  used  at  many  localities.  It  is  adaptable  to  a  wider 
range  of  clays  than  any  of  the  others,  and  possesses  the  advantage  of 
producing  not  only  a  brick  of  very  homogeneous  structure,  but  one  that 
is  rarely  affected  by  frost  action. 


228  CLAYS 

Stiff-mud  process.— With  this  method  (PL  XII,  Fig.  2,  and  Fig.  44.), 
the  clay  is  tempered  with  less  water  and  consequently  is  much  stiffer. 
The  principle  of  the  process  consists  in  taking  the  clay  thus  prepared  and 
forcing  it  through  a  die  in  the  form  of  a  rectangular  bar,  which  is  then 
cut  up  into  bricks.  The  most  general  form  of  the  stiff-mud  machine, 
known  as  the  auger  machine,  is  that  of  a  cylinder  closed  at  one  end, 
but  at  the  other  end  tapering  off  into  a  rectangular  die  whose  cross- 
section  is  the  same  as  either  the  end  or  the  largest  side  of  a  brick.  Within 
this  cylinder,  which  is  set  in  a  horizontal  position,  there  is  a  shaft, 
carrying  blades  similar  to  those  of  a  pug-mill,  but  at  the  end  of  the 
shaft  nearest  the  die  there  is  a  tapering  screw.  The  die  is  heated  by 
steam  or  lubricated  by  oil  on  its  inner  side,  in  order  to  facilitate  the 
flow  of  the  clay  through  it. 

The  tempered  clay  is  charged  into  the  cylinder  at  the  end  farthest 
from  the  die,  is  mixed  up  by  the  revolving  blades,  and  at  the  same  time 
it  is  moved  forward  until  seized  by  the  screw  and  pushed  through  the  die. 
Since  this  involves  considerable  power,  it  results  in  a  marked  compression 
of  the  clay,  and  there  is  also  some  friction  between  the  sides  of  the  bar 
and  the  interior  of  the  die,  causing  the  center  of  the  stream  of  clay  to 
move  faster  than  the  outer  portion.  Excessive  friction  between  die 
surface  and  clay  is  likely  to  cause  the  latter  to  tear  on  the  edges, 
producing  serrations  like  the  teeth  of  a  saw.  The  effect  of  the  screw  at 
the  end  of  the  shaft,  together  with  the  differential  velocities  within  the 
stream  of  clay,  also  produces  a  laminated  structure  in  the  brick,  which  is 
often  greatest  in  highly  plastic  clays,  but  is  sometimes  marked  in  clays  of 
only  moderate  plasticity  when  machines  of  a  particular  structure  are 
used. 

The  brick  made  in  auger  machines  are  either  end-cut  or  side-cut, 
depending  on  whether  the  area  of  the  cross-sections  of  the  bar  of  clay 
corresponds  to  the  end  or  side  of  a  brick,  and  consequently  the  mouth 
of  the  die  varies  in  size  and  shape.  The  auger  machine  is  probably  used 
more  extensively  at  the  present  day  than  either  the  soft-mud  or  dry- 
press  machine,  especially  for  making  paving-brick.  It  has  a  large 
capacity  and  can  produce  45,000  or  even  60,000  brick  in  ten  hours,  the 
output  of  the  machine  being  sometimes  increased  by  the  use  of  double  or 
even  triple  dies,  though  this  is  not  a  desirable  practice. 

As  the  bar  of  clay  issues  from  the  machine  it  is  received  on  the  cutting- 
table,  where  it  is  cut  up  into  bricks. 

The  stiff-mud  process  is  adapted  mainly  to  clays  of  moderate  plas- 
ticity. The  stiff-mud  brick,  like  the  soft-mud  ones,  can  be  re-pressed, 
and  many  face  brick  are  now  made  by  this  process. 


KINDS  OF  CLAYS  231 

Dry-press  (PL  XIII)  and  semi-dry-press  process. — This  process  is 
commonly  used  for  the  production  of  front  brick,  but  in  some  States  is 
extensively  employed  even  for  common-brick  manufacture.  The  clay  is 
powdered  and  then  pressed  into  steel  molds  in  a  dry  or  nearly  dry  condi- 
tion. In  order  to  prepare  the  clay  for  disintegration,  it  is  usually  stored 
in  sheds  for  some  time  before  being  used,  and  is  then  broken  up  either 
in  a  disintegrator  or  a  dry  pan  before  passing  to  the  screen,  which  is  com- 
monly from  12  to  16  mesh.  The  molding-machine  consists  of  a  steel 
frame  of  varying  height  and  heaviness,  with  a  delivery-table  about  3 
feet  above  the  ground,  and  a  press-box  sunk  into  the  rear  of  it.  The 
charger  is  connected  with  the  clay-hopper  by  means  of  a  canvas  tube, 
and  forms  a  framework  which  slides  back  and  forth  over  the  molds. 
It  is  filled  on  the  backward  stroke,  and  on  its  forward  stroke  lets  the 
clay  fall  into  the  mold-box.  As  the  charger  recedes  to  be  refilled,  a 
plunger  descends,  pressing  the  clay  into  the  mold;  but  at  the  same  time 
the  bottom  of  the  mold,  which  is  movable,  rises  slightly,  and  the  clay 
is  subjected  to  great  pressure,  which  may  be  repeated  after  a  moment's 
interval.  The  plunger,  then  rises,  while  the  bottom  of  the  mold  also 
ascends,  with  the  freshly  molded  bricks,  to  a  level  with  the  delivery- 
table.  These  are  then  pushed  forward  by  the  charger  as  it  advances  to 
refill  the  molds. 

The  faces  of  the  mold  are  of  hard  steel  and  heated  by  steam  to 
prevent  adherence  of  the  clay.  Air-holes  are  also  made  in  the  dies  to 
permit  the  air,  which  becomes  imprisoned  between  the  clay  particles, 
to  escape.  If  this  were  not  done,  the  air  in  the  clay  would  be  com- 
pressed, and  when  the  pressure  was  released,  its  expansion  would 
tend  to  split  the  brick.  At  several  localities  in  the  United  States  an 
hydraulic  dry-press  machine  is  used,  in  which  the  gradually  applied 
pressure  is  produced  by  a  pair  of  hydraulic  rams  acting  from  above 
and  below. 

The  advantages  claimed  for  the  dry-press  process  are  that  in  one 
operation  it  produces  a  brick  with  sharp  edges  and  smooth  faces.  There 
is  practically  no  water  to  be  driven  off,  as  the  clay  has  been  pressed  in  a 
nearly  dry  condition,  hence  drying  is  done  more  rapidly.  When  hard- 
burned,  dry-pressed  bricks  are  as  strong  as  others,  but  on  account  of  the 
method  of  molding  they  often  show  a  granular  structure. 

The  capacity  of  a  dry-press  machine  is  about  the  same  as  that  of  a 
soft-mud  one,  provided  six  bricks  are  molded  at  a  time.  Two-  and 
four-mold  machines  are,  however,  also  made.  The  initial  cost  of  the 
machinery  is  considerable,  although  this  may  be  more  than  offset  by  the 
saving  in  drying. 


232  CLAYS 

Re-pressing.— Many  soft-mud  and  stiff-mud  brick  that  are  to  be 
used  for  fronts  are  improved  in  appearance  and  often  in  density  by  re- 
pressing, an  operation  which  smoothens  the  surface  and  straightens  and 
sharpens  the  edges  of  the  product,  as  well  as  sometimes  increasing  the 
strength.  A  re-pressing  machine  is  shown  in  PI.  XIV,  Fig.  1. 

The  change  in  volume  that  occurs  in  a  brick  in  re-pressing  can  be 
seen  from  the  following  measurements  of  a  paving-brick : 

Before  re-pressing,  8f  by  4|  by  3^  inches,  =  H9f  cubic  inches. 
After  re-pressing,  8H  by  4|  by  3£  inches,  =  109^  cubic  inches. 

Drying 

Bricks  made  by  either  the  stiff-mud  or  soft-mud  process  have  to  be 
freed  from  most  of  their  water  of  tempering  before  they  can  be  burned. 

Open  yards. — These  are  used  at  most  soft-mud  brick-plants,  and 
are  simply  smooth  flat  floors  of  earth  or  brick,  on  which  the  bricks  are 
dumped  as  soon  as  molded,  and  allowed  to  dry  in  the  sun.  At  some 
yards  the  drying-floor  is  partly  covered. 

Pallet  driers. — These  are  covered  frames  for  holding  the  boards  or 
"  pallets  "  on  which  the  bricks  are  dumped  from  the  mold  at  the  machine. 
They  are  used  at  many  soft-mud  yards  and  even  some  stiff-mud  plants, 
and  possess  the  advantage  of  cheapness,  large  capacity,  economy  of 
space,  and  protection  against  rain. 

One  disadvantage  of  the  above  method  is  that  the  driers  can  not  be 
used  in  cold  weather.  Dampness  in  summer  may  also  interfere  with 
them,  and  therefore  sunlight  and  wind  are  usually  the  most  favorable 
weather  conditions.  Some  clays  are  quite  susceptible  to  air-currents, 
however,  and  crack  easily  when  exposed  to  them. 

Drying-tunnels. — Many  brickmakers  dry  their  product  by  this 
method,  especially  if  they  continue  in  operation  throughout  the  year. 
With  this  system  the  bricks,  after  molding,  are  piled  on  cars,  which 
are  run  into  an  artificially  heated  tunnel  (Fig.  45).  Several  of  these 
tunnels  are  generally  constructed  side  by  side,  and  the  green  bricks  are 
run  in  at  the  cooler  end,  and  pushed  along  slowly  to  the  warmer  end, 
where  they  are  removed,  this  passage  through  the  tunnel  requiring 
commonly  from  24  to  48  hours.  The  tunnel  driers  used  at  different 
localities  differ  chiefly  in  the  manner  in  which  they  are  heated,  the 
following  methods  being  employed: 

1.  Parallel  flues  underneath  and  heated  by  fireplaces  at  one  end. 
2.  By  steam  heat,  the  pipes  being  laid  on  the  floor  or  sides  of  the  tunnel 
or  both.  3.  By  hot  air,  the  latter  being  supplied  from  cooling-kilns, 


PLATE   XIII 


Dry-press  brick-machine.     (After  H.  Ries,  N.  Y.  State  Mus., 
Bull.  35,  p.  665,  1900.) 


233 


KINDS  OF  CLAYS 


235 


o 

I" 


236  CLAYS 

or  by  passing  the  outer  air  over  steam-coils  before  it  is  drawn  through 
the  tunnel  by  natural  draft  or  fan.  If  the  air  is  too  hot,  cooler  air  is 
mixed  with  it  before  it  enters  the  drier.  The  temperature  to  which 
tunnels  are  heated  varies,  and  in  most  cases  is  not  over  120°  C.  (250°  F.). 

Floor  driers. — Floor  driers  are  used  at  some  brick-works,  although 
their  application  is  more  extended  at  fire-brick  works.  They  are  made 
of  brick,  and  have  flues  passing  underneath  their  entire  length,  from 
the  fireplace  at  one  end  to  the  chimney  at  the  other.  Such  floors  are 
cheap  to  construct,  but  the  distribution  of  the  heat  under  them  is  rather 
unequal,  and  a  large  amount  of  labor  is  required  to  handle  the  material 
dried  on  them. 

In  some  cases  drying-racks  are  set  up  on  the  top  of  the  kiln. 


Burning 

Kilns. — Bricks  are  burned  in  a  variety  of  kilns,  ranging  from  tempo- 
rary structures,  which  are  torn  down  after  each  lot  of  brick  is  burned 
(PL  XIV,  Fig.  2),  to  patented  or  other  permanent  forms  of  complicated 
design.  They  are  built  on  one  of  two  principles,  either  up-draft  or  down- 
draft.  In  the  former  the  heat  from  the  fire-boxes  at  the  bottom  passes 
directly  into  the  body  of  the  kiln  and  up  through  the  wares,  escaping 
from  suitable  chimneys  or  openings  at  the  top.  In  the  latter  the  heat 
from  the  fire-boxes  is  conducted  first  to  the  top  of  the  kiln  chamber,  by 
means  of  suitable  flues  on  the  interior  wall,  and  then  down  through  the 
wares;  being  carried  off  through  flues  in  the  bottom  of  the  kiln  to  the 
stack  (PL  XV,  Fig.  2).  The  down-draft  system  is  growing  in  favor, 
as  the  burning  can  be  regulated  better.  Furthermore,  since  the  bricks 
at  the  top  receive  the  greatest  heat,  and  these  at  the  bottom  the  least, 
there  is  less  danger  of  the  bricks  in  the  lower  courses  being  crushed  out 
of  shape  if  heated  too  high. 

The  amount  of  heat  required  for  burning  brick  will  vary  with  the 
clay  and  the  color,  density  or  degree  of  hardness  desired,  the  same 
clay  giving  different  results  when  burned  at  different  temperatures. 
Common  bricks  are  rarely  burned  any  higher  than  cone  05,  and  usually 
not  above  cone  010,  while  pressed  brick  are  frequently  fired  to  cone 
7  or  8,  because  the  clays  generally  used  have  to  be  burned  to  that  point 
to  render  them  hard. 

Up-draft  kilns. — The  simplest  type  of  kiln  with  rising  draft  is  known 
as  the  "scove-kiln"  (PL  XIV,  Fig.  2,  and  PL  XV,  Fig.  1),  which  is  in 
use  at  many  yards  making  common  brick,  and  is  of  a  temporary  character. 
The  bricks  are  set  in  large  rectangular  blocks  from  38  to  54  courses 


PLATE   XIV 


FIG.   1. — A  steam-power  re-press.     The  bricks  on  the  belt  are  being  brought  from 
the  stiff-mud  machine.     (Photo  by  H.  Ries.) 


FIG.    2. — Setting    brick   for    a    scove-kiln.     (After    H.    Ries,    N.   J.   Geol.    Surv., 
Fin.  Rept.,  VI,  p.  240,  1900.) 

237 


--  -e " 

O     THE 

ERSITY  ) 


OF 


KINDS  OF  CLAYS  239 

high,  depending  on  the  kind  of  clay.  In  building  up  the  mass  a  series 
of  parallel  arches  is  left  running  through  the  mass  from  side  to  side,  and 
with  their  centers  about  two  feet  apart.  After  the  bricks  are  set  up  they 
are  surrounded  by  a  wall  two  courses  deep  of  " double-coal"  brick,  and 
the  whole  outside  of  the  mass  daubed  with  wet  clay  to  prevent  the 
entrance  of  cold  air  during  burning.  The  top  of  the  kiln  is  then  closed 
by  a  layer  of  bricks  laid  close  together  and  termed  the  platting.  Kilns 
of  this  type  involve  little  cost  except  the  labor  of  building.  They  are, 
however,  adapted  only  to  common  brick,  and  are  not  capable  of  being 
heated  to  a  high  temperature. 

The  so-called  Dutch  kilns  are  a  slight  improvement  over  the  scove- 
kilns,  since  they  have  permanent  side  walls,  and  so  yield  somewhat 
better  results,  for  they  heat  up  better  and  admit  less  cold  air. 

Many  common  brick  and  nearly  all  front  brick,  however,  are  burned 
in  kilns  that  are  walled  and  roofed,  with  a  door  at  each  end  for  filling 
and  emptying.  They  are,  therefore,  far  more  reliable,  capable  of  better 
regulation,  attain  higher  temperatures,  and  are  both  up-draft  and  down- 
draft.  The  fuel  used  is  sometimes  wood,  but  mostly  coal,  not  a  few 
manufacturers  employing  anthracite  in  part.  With  coal,  the  fuel  is 
sometimes  placed  on  grate-bars  or  on  the  floor  of  the  hearth.  In  plan 
they  are  either  rectangular  or  circular.  The  bricks  are  set  in  much  the 
same  way  as  in  the  others. 

Down-draft  kilns. — In  these  the  heat  from  the  fires  is  conducted 
first  to  the  top  of  the  kiln-chamber  by  means  of  suitable  flues  on  the 
inner  wall  of  the  kiln,  and  then  down  through  the  ware,  being  carried 
off  through  flues  in  the  bottom  of  the  kiln  to  the  stack.  With  this 
system  the  burning  can  be  regulated  better,  and  there  is  less  loss  from 
cracked  and  overburned  brick.  Furthermore,  since  the  bricks  at  the 
top  receive  the  greatest  heat,  and  those  at  the  bottom  the  least,  there 
is  less  danger  of  the  bricks  in  the  lower  courses  being  crushed  out  of 
shape.  Down-draft  kilns  are  either  circular  or  rectangular  in  form. 
The  latter,  which  have  greater  capacity  and  are  more  economical  of 
space,  are  employed  commonly  for  burning  brick,  while  the  former  are 
preferred  for  drain-tile,  sewer-pipe,  or  stoneware. 

There  are  a  number  of  different  types  of  down-draft  kilns,  which  differ 
in  the  arrangement  and  structure  of  the  flues,  arrangement  of  the  fire- 
place, etc. 

Continuous  kilns  (PI.  XVI,  Fig.  2). — These  were  originally  designed 
to  utilize  the  waste  heat  from  burning.  Many  types  have  appeared, 
some  of  which  are  patented,  but  the  principle  of  all  is  the  same.  It 
consists  essentially  in  having  a  series  of  chambers  arranged  in  a  line, 


240  CLAYS 

circle,  or  oval,  and  connected  with  each  other  and  also  with  a  central 
stack  by  means  of  flues.  Each  chamber  holds  about  22,000  bricks.  In 
starting  the  kiln,  a  chamber  full  of  bricks  is  first  fired  by  means  of  exterior 
fire-boxes,  and  while  the  water-smoke  or  steam  is  passing  off  the  vapors 
are  conducted  to  the  stack,  but  as  soon  as  this  ceases  the  heat  from  the 
chamber  first  fired  is  conducted  through  several  other  chambers  ahead 
of  it,  before  it  finally  passes  to  the  stack.  In  this  manner  the  waste 
heat  from  any  chamber  is  used  to  heat  the  others.  When  any  one 
compartment  becomes  red  hot,  fuel  in  the  form  of  coal-slack  is  added 
through  small  openings  in  the  roof,  which  are  kept  covered  by  iron 
caps. 

As  soon  as  one  chamber  has  reached  its  maximum  temperature,  the 
next  two  or  three  ahead  of  it  are  being  heated  up,  while  those  behind  it 
are  cooling  down.  A  wave  of  maximum  temperature  is  therefore  con- 
tinually passing  around  the  kiln.  It  is  thus  possible  to  be  burning 
brick  in  certain  chambers,  filling  others,  and  emptying  still  others,  all 
at  the  same  time,  making  the  process  a  continuous  one.  Continuous 
kilns  are  employed  in  many  states  for  burning  common  brick  with 
considerable  success. 


Sewer-pipe  Manufacture 

While  some  works  use  a  soft  clay  for  sewer-pipe,  the  largest  factories 
in  the  United  States,  namely,  those  located  in  Ohio,  run  chiefly  on  shale, 
to  which  a  certain  amount  of  refractory  clay  is  sometimes  added.  The 
material  therefore  requires  crushing  before  tempering.  Dry  pans  (p. 
219)  are  used  for  this  purpose.  The  ground-clay  is  then  screened  and 
mixed  in  pug-mills  (p.  220),  wet  pans  (p.  220),  or  chaser-mills  (p.  265). 

Sewer-pipes  are  made  in  a  special  form  of  press  (Figs.  46  and  47,  and 
PI.  XVII,  Fig.  1)  consisting  of  two  cylinders,  connected  with  a  continuous 
piston  and  placed  one  above  the  other.  The  upper  is  the  steam  and  the 
lower  the  clay  cylinder.  The  size  ratio  of  these  twro  cylinders  varies 
from  1  :  2  to  1  :  3.1  "The  piston  is  propelled  by  the  admission  of  steam 
to  the  upper  cylinder,  giving  it  a  downward  movement  which  presses 
the  clay  through  a  die  at  the  bottom  of  the  lower  cylinder.  The  action 
is  then  intermittent,  the  piston  receding  when  it  has  reached  its  length 
of  stroke  and  a  supply  of  clay  is  needed. 

"The  clay  previously  prepared  and  in  plastic  condition  is  brought 
to  the  press  on  a  moving  belt.  Each  time  the  piston  recedes,  the  cylinder 

1  Beyer  and  Williams,  hi.  (Jeol.  Surv.,  XIV,  p.  214,  1904. 


PLATE   XV 


FIG.  1. — Side  view  of  a  scove-kiln  for  burning  common  brick,  exterior  daubed 
over  with  wet  clay.  The  firing-holes  are  shown  at  bottom  of  one  side.  (After 
H.  Ries,  N.  J.  Geol.  Surv.,  Fin.  Kept.,  VI,  p.  240,  1904.) 


FIG.  2. — Down-draft  kilns.      (Photo  loaned  by  Robinson  Clay-product  Co.) 

241 


PLATE   XVI 


FIG.  1. — Interior  view  of  circular  down-draft  kiln.     (Photo  loaned  by  Robinson 
Clay-product  Manufacturing  Co.) 


FIG.  2. — Haight  continuous  kiln.     (After  H.  Ries,  N.  Y.  State  Mus.,  Bull.  35, 

p.  679,  1900.) 

243 


KINDS  OF  CLAYS 


245 


is  filled  with  clay  by  throwing  this  belt  into  motion.  The  die  which 
forms  the  pipe  consists  of  a  central  cone  and  an  outer  die  or  bell,  the 
space  between  the  cone  and  bell  determining  the  thickness  of  the  wall 
of  the  pipe.  By  changing  these  the  various  sizes  of  sewer-pipe  are 


FIG.  46. — Side  elevation  of  a  sewer-pipe  press. 

made.  It  has  been  found  of  advantage  to  have  the  issue,  or  the  dis- 
tance through  which  the  clay  must  travel  between  the  dies,  compressed 
to  its  maximum  thickness,  quite  long.  J.  E.  Minter l  recommends 
an  issue  of  not  less  than  three  inches  for  dies  smaller  than  eight  inches 

1  Brick,  XV11I,  No.  1,  p.  48. 


246 


CLAYS 


and  not  below  four  inches  for  dies  over  eight  inches  in  diameter.  The 
basis  for  this  recommendation  is  that  where  the  issue  is  short,  blebs 
of  air  imprisoned  in  the  clay  will  remain  and  are  apt  to  form  blisters 
on  the  pipes,  while  with  a  long  issue  the  air  will  back  upwards  through 


FIG.  47.— Front  elevation  of  a  sewer-pipe  press. 

the  loose  clay  and  escape  in  the  direction  of  least  resistance  rather  than 
remain  in  the  clay." 

Beneath  the  die  is  the  pipe-table  which  receives  the  pipe  as  it  issues 
from  the  cylinder.  The  table  is  supported  by  a  vertical  rod  which  is 
kept  in  perfect  alignment  with  the  center  of  the  cylinder.  The  table 


KINDS  OF  CLAYS  247 

is  raised  and  lowered  by  weights  which  may  be  so  adjusted  as  to  counter- 
balance. After  the  pipe  is  forced  out  the  desired  length  it  is  cut  by 
hand,  by  wire,  or  automatically  by  means  of  a  power  cutter,  the  last 
consisting  of  a  knife  edge  in  the  lower  part  of  the  cylinder,  which  is 
thrust  out  and  given  a  circular  motion  that  severs  the  pipe  when  the 
cutting  mechanism  is  thrown  into  gear.  The  length  of  stroke  of  the 
piston  and  therefore  the  maximum  length  of  the  pipe  is  about  four 
feet.  The  diameter  of  the  pipes  ranges  from  three  or  four  inches  to 
three  feet. 

Special  shapes,  such  as  traps,  sockets,  elbows,  and  trees,  are  usually 
made  by  hand  in  plaster  molds,  and  require  careful  drying.  At  times 
Y  shapes  can  be  made  by  cutting  two  straight  pieces  on  the  slant  and 
joining  them  together  with  wet  clay. 

Sewer-pipes  are  dried  on  floors,  heated  by  steam-pipes,  and  burned 
in  down-draft  kilns.  For  burning  they  are  stood  on  end  and  salt-glazed. 

All  defects,  such  as  iron  spots,  blisters,  imperfect  glazing,  or  warp- 
ing, cause  the  product  to  be  placed  among  seconds. 

Drain-tile 

Drain-tile  are  made  in  several  styles  as  follows: 

Horseshoe- tile,  of  horseshoe-shaped  cross -section. 
Sole-tile,  cylindrical  with  a  flat  base. 
Pipe-tile,  with  cylindrical  cross-section. 

For  the  making  of  drain-tile  the  clay  should  be  thoroughly  tempered 
before  molding,  this  being  commonly  done  in  a  pug-mill  (p.  220).  Mold- 
ing is  usually  done  in  some  form  of  stiff-mud  machine,  the  cylinder 
of  clay  as  it  issues  from  the  die  being  cut  up  into  the  desired  lengths. 
Drying  is  commonly  done  on  pallet-racks  (p.  232),  such  as  are  used  for 
common  bricks,  or  it  may  also  be  done  in  tunnels.  The  burning,  which 
is  usually  done  at  a  low  temperature,  presents  no  special  difficulties, 
and  is  done  in  a  variety  of  kilns,  the  tile  being  often  burned  with  com- 
mon brick. 

Hollow  Ware  for  Structural  Work 

Under  this  heading  are  included  fireproofing,  terra-cotta  lumber, 
hollow  blocks  and  hollow  bricks.  These  are  all  hollow  (PL  XVII, 
Fig.  2),  being  molded  through  a  stiff-mud  die  and  may  contain  one 
or  more  cross  webs  or  partitions  to  give  them  strength.  Fireproofing 


248  CLAYS 

is  the  term  applied  to  those  forms  used  in  the  construction  of  floor- 
arches,  partitions,  and  wall-furring  for  columns,  girders,  and  other 
purposes  in  fireproof  buildings.  Terra-cotta  lumber  is  a  form  of  fire- 
proofing  that  is  soft  and  porous,  owing  to  the  addition  of  a  large  per- 
centage of  sawdust  to  the  clay.  The  former  burns  off  in  the  kiln,  thus 
leaving  the  material  so  soft  and  porous  that  nails  can  be  driven  into 
it.  It  is  used  chiefly  for  partitions.  Hollow  blocks  are  used  for  exterior 
walls,  in  both  fireproof  and  non-fireproof  buildings.  They  are  of  rec- 
tangular outline.  Hollow  brick  are  like  hollow  blocks  in  form,  but  no 
larger  than  ordinary  building-bricks. 

A  number  of  different  shapes  and  sizes  of  fireproofing  are  made, 
and  while  the  majority  of  them  agree  in  being  12  inches  long  the  other 
two  dimensions  may  vary.  Thus  of  the  blocks  which  are  12  inches 
long,  the  other  dimensions  may  be  6  by  3  in.,  6  by  4  in.,  6  by  5  in., 
6  by  6  in.,  6  by  7  in.,  etc.,  or  perhaps  3  by  8  in.,  or  3  by  12  in.,  etc.  A 
large  number  of  the  fireproof  shapes  made  are  for  floor-arches,  and  in 
such  cases  the  architect  commonly  specifies  the  depth  of  the  arch,  while 
the  width  of  the  blocks  is  governed  by  the  width  of  the  span.  The 
weight  of  the  arch  will  depend  on  its  depth. 

Thus,    6-inch   floor-arches   weigh  about  25  pounds  per  square  foot. 


7   " 

it        tt           tt 

tt       2g      tt 

tt         «  c 

10   " 

tt        tt           tt 

tt       35      tt 

«  «         « 

12    " 

tt        tt           tt 

tt       42      tt 

it         it 

3    " 

book-tile              '  ' 

tt       15      tt 

tt         1  1 

3    " 

partition-tile       '  ' 

tt       15      tt 

tt         it 

6   " 

tt          it         it 

tt       21       "         " 

tt         ti 

8   " 

tt          .<          tt 

28      " 

it         tt 

2    " 

wall  furring         '  ' 

8.5  " 

K         it 

3   " 

«         tt               tt 

"       10.5  " 

it         n 

2   " 

column  covering  " 

"       13      " 

it         tt 

3    " 

it            t  t       it 

15      " 

tt         it 

The   cost   of  fireproofing   is   commonly  figured   by   the   ton. 

Hollow  blocks  are  usually  made  in  8-inch  lengths,  but  vary  in  their 
other  dimensions,  being  4  by  16  in.,  6  by  16  in.,  8  by  16  in.,  10  by  16  in., 
12  by  16  in.,  etc.  They  are  used  quite  extensively  in  the  Central  States, 
but  not  so  much  in  the  Eastern  ones.  Hollow  blocks  are  made  with 
either  smooth,  corrugated,  or  ornamental  surfaces. 

Sizes  8  by  4  by  16  in.  are  sold  for  about  $0.07 each,  and  8  by  8  by  16  in. 
at  $0.10  each.  Hollow  bricks  are  often  used  for  the  interior  course 
of  exterior  walls,  and  the  plaster  can  be  laid  directly  on  them  with- 
out the  use  of  lathing. 


PLATE   XVII 


FIG.  1. — Molding   30-inch   sewer-pipe  in  pipe-press.       (Photo  loaned  by  Robinson 

Clay-product  Co.) 


FIG.   2. — Some    forms   of   fireproofing    made   by   stiff-mud  machine.      (Photo  by 
C.  M.  Doyle  in  N.  Y.  State  Museum,  Bull.  35,  p.  775,  1900.) 

249 


KINDS  OF  CLAYS  251 

In  some  States  shales  are  used  for  making  hollow  ware,  while  in 
others  plastic  clays  are  employed.  Calcareous  clays  are  undesirable 
as  being  unsuited  to  the  production  of  a  vitrified  ware. 

The  clays  used  for  making  fireproofing  have  been  referred  to  on 
p.  192. 

Manufacture. — The  method  of  preparation  used  for  making  hol- 
low blocks  or  fireproofing  is  essentially  the  same  as  that  employed 
in  the  manufacture  of  stiff-mud  bricks.  Shales  are  sometimes  first 
ground  in  a  dry  pan  (p.  219)  or  disintegrator  (p.  219)  and  then  screened, 
followed  by  mixing  in  a  pug-mill  (p.  220) ;  or  a  wet  pan  (p.  220)  may  do 
the  combined  work  of  crushing  and  tempering.  Molding  is  done  in  a 
stiff-mud  machine  (p.  228),  care  being  necessary  to  have  the  clay  suffi- 
ciently plastic  to  permit  its  flowing  freely  from  the  die  and  prevent 
tearing  on  the  corners  or  edges. 

The  die  is  of  a  special  type,  which  emits  a  hollow  tube  with  cross- 
partitions,  and  the  cutting-table  is  likewise  sometimes  of  a  specialized 
type,  so  designed  that  as  the  brick  reaches  the  end  of  the  table  it  is 
turned  to  an  upright  position  to  facilitate  handling. 

Hollow  blocks  and  fireproofing  are  dried  on  racks  (p.  232)  in  tunnel- 
driers  (p.  232),  or  even  on  heated  floors,  the  last  being  the  method  most 
commonly  used. 

When  hot  floors  are  used  they  are  heated  by  steam-pipes  passing 
under  them  or  around  the  walls  of  the  drying-room. 

In  burning  any  of  these  shapes  they  are  stood  on  end,  and  the 
smaller  ones  are  sometimes  burned  in  the  same  kilns  with  brick. 

Williams1   gives   the  following   advantages  for  hollow  blocks: 

Lightness. — Sufficient  strength,  to  insure  a  large  factor  of  safety 
in  any  common  building  construction  Amount  of  clay  required  from 
one  third  to  one  half  that  necessary  for  solid  brick.  Smaller  expense 
of  transportation  due  to  decreased  weight  of  product.  Full  protection 
against  dampness  and  temperature.  Possibility  of  terra-cotta  decora- 
tion on  exterior  of  block.2 

Conduits 

Manufacture. — Conduits  form  a  line  of  clay-products,  the  use  of 
which  has  greatly  increased  in  the  last  few  years.  These  are  hollow 
blocks  of  varying  length,  having  sometimes  several  cross-partitions 
and  rounded  edges,  and  are  used  as  pipes  for  electrical  cables  and  wires 

1  la.  Geol.  Surv.,  XIV,  p.  213. 

2  See  E.  G.  Durant.     Hollow  Building-blocks.     Published  by  American  Clay- 
working  Machinery  Co.,  Bucyrus,  O.     (No  date.) 


252  CLAYS 

below  ground.  On  this  account  they  have  to  be  hard-burned  with 
dense  body,  and  are  salt-glazed. 

The  clays  used  are  similar  to  those  employed  for  making  fireproofing, 
although  they  are  somewhat  more  carefully  selected  with  regard  to 
plasticity  and  freedom  from  pyrite  and  limonite  lumps.  They  must 
also  burn  dense  at  a  moderate  temperature. 

The  clays  are  prepared  in  essentially  the  same  manner  as  for  hol- 
low blocks,  and  are  molded  in  auger  stiff-mud  machines.  They  are 
then  removed  from  the  cutting-table  on  a  pallet  and  placed  on  a  stand, 
where  the  ends  are  trimmed  smooth  before  the  pieces  are  taken  to  the 
drying-floor  or  drying-tunnel.  In  drying,  the  conduits  are  stood  on 
end.  The  burning  is  commonly  done  in  down-draft  kilns,  between 
cones  8  and  9,  although  some  manufacturers  burn  lower  than  this.  The 
average  shrinkage  that  takes  place  in  a  long  conduit  is  about  as  follows:1 
Length,  freshly  molded,  39  inches;  length,  air-dried,  37£  inches;  length, 
burned,  35  inches. 

There  has  been  a  great  demand  for  conduits  in  many  cities  during 
the  last  few  years,  many  being  used  in  New  York  City  especially,  in 
the  construction  of  the  rapid-transit  subway,  and  some  large  plants 
are  run  almost  exclusively  on  this  line  of  work. 

Conduits  are  also  occasionally  made  at  the  fireproofing  factories. 

Fire-brick 

Most  fire-brick  makers  employ  a  mixture  of  several  grades  of  clay, 
to  which  there  is  added  a  certain  percentage  of  ground  fire-brick  or 
even  coarse  quartz.  These  ingredients  are  sometimes  ground  in  a 
dry  pan  (p.  219)  or  disintegrator  (p.  219),  then  screened,  and  tempered 
in  a  pug-mill  (p.  220).  At  some  plants  a  wet  pan  (p.  220)  combines  the 
crushing  and  tempering  operation.  Where  soft  clays  exclusively  are 
used,  the  tempering  is  occasionally  done  in  a  ring-pit  (p.  220). 

Fire-bricks  were  originally  molded  entirely  by  hand,  and  some 
manufacturers  still  cling  to  this  method,  but  many  now  employ  the 
soft-mud  (p.  220)  or  stiff-mud  machine  (p.  228).  In  all  these  methods 
the  brick  requires  re-pressing  after  it  has  been  drying  for  a  few  hours. 
A  few  works  manufacture  dry-press  (p.  231)  brick,  and  for  some  pur- 
poses these  may  be  desirable,  but  they  are  not  regarded  as  altogether 
satisfactory.  Drying  is  generally  done  on  brick  floors,  heated  by  flues 
passing  underneath  them,  but  some  manufacturers  prefer  dry  ing- tun- 
nels (p.  232). 

1  N.  J.  Geol.  Surv.,  Final  Kept.,  VI,  p.  284,  1904. 


KINDS   OF  CLAYS 


253 


Most  fire-brick  makers  burn  their  brick  in  down-draft  kilns,  but 
there  is  a  remarkable  difference  in  the  temperature  reached,  this  in 
the  United  States  ranging  from  cones  5  to  18. 

Fire-bricks  are  made  in  many  different  shapes,  and  vary  greatly 
in  their  density,  hardness,  and  texture,  according  to  the  conditions  under 
which  they  are  to  be  used.  For  abrasive  resistance  they  must  be  hard, 
to  resist  corrosion  they  must  be  dense,  while,  for  resistance  to  high  heats 
and  changes  of  temperature,  porosity  and  coarseness  are  of  importance.  ' 

1    23456789  10      12      14      16     IE      20      22      24      2ft      28      30     32      ?l-     36      38      40      42     44s 


1    2    3  4    5   6  7   8   9  10      12      14      16      18      20      22     24      26      28      30      32      34     36      38     40      42     44 

If  umber  of  Analysis 

FIG.  48. — Graphic  representation  of  composition  and  fusibility  of  some  domestic 

fire-brick.     (After  Weber.) 

The  influence  of  texture  and  composition  on  refractoriness  has  been 
well  set  forth  by  the  experiments  by  Weber,1  which  are  graphically 
illustrated  in  Fig.  48. 

From  these  tests  he  concluded  that  the  refractoriness  of  a  fire-brick 
depends  on  the  total  quantity  of  fluxes  present,  the  silica  percentage, 
and  the  coarseness  of  grain. 

1  Trans.  Amer.  Inst.  Min.  Eng.,  Sept.,  1904. 


254  CLAYS 

Roofing-tile 

Although  used  for  many  years  abroad,  the  manufacture  of  roofing- 
tile  has  not  been  very  extensively  developed  in  the  United  States,  but 
its  growth  in  the  last  decade  is  nevertheless  gratifying. 

Roofing-tile  are  made  in  the  following  shapes: 

Shingle-tile,  which  are  perfectly  flat,  and  laid  on  the  roof  in  the 
same  manner  as  slate. 

Roman  tile,  of  semi-circular  cross- sect  ion,  and  laid  with  the  con- 
vex and  concave  side  up  alternately,  so  that  one  straddles  two  others- 

Interlocking-tile,  with  grooves  and  ridges  which  fit  into  each  other, 
thus  locking  the  tiles  together. 

The  first  are  usually  vitrified,  the  others  may  or  may  not  be,  and 
if  porous  are  often  salt-glazed. 

The  crushing  and  preparation  of  the  clay  is  done  by  the  same  methods 
as  are  used  for  making  stiff-mud  brick.  Shinge-tile  and  Roman  tile  can 
be  molded  by  forcing  a  ribbon  of  clay  from  an  auger-machine  die,  but 
interlocking-tile  are  made  by  repressing  slabs  of  the  tempered  clay  in  a 
special  form  of  machine.  (PL  XVIII,  Fig.  1.)  The  tiles  are  dried  in  tun- 
nels and  burned  in  up-  or  down-draft  kilns  to  the  proper  temperature. 

Terra-cotta 

The  term  terra-cotta  is  applied  to  those  clay-products  used  for  struc- 
tural decorative  work,  and  which  cannot  be  formed  by  machinery. 
They  are  therefore  to  be  molded  by  hand.  The  requisite  qualities  of 
terra-cotta  clays  have  been  referred  to  on  p.  182.  Most  factories  use 
not  only  a  mixture  of  several  clays,  but  add  in  a  variable  quantity  of 
grog,  i.e.,  ground  fire-brick,  terra-cotta,  or  sewer-pipe.  The  object  of 
using  such  a  mixture  is  to  produce  a  body  of  the  proper  plasticity, 
shrinkage,  and  density  after  burning,  and  the  color  of  the  body  is  of 
no  great  importance,  since  the  color  is  applied  superficially. 

Manufacture. — The  manufacture  of  terra-cotta  stands  on  a  much 
higher  plane  in  ceramic  technology  than  it  did  a  few  years  ago,  so  that 
the  number  of  colors  now  made  is  much  greater;  and  attention  has 
also  been  directed  towards  producing  effects  which  closely  imitate  differ- 
ent kinds  of  building  stones,  as  well  as  increasing  the  complexity  in 
the  designs  which  can  be  executed.  Indeed,  the  use  of  terra-cotta  for 
exterior  decoration  has  met  with  such  success  that  but  few  modem 
buildings  of  large  size  are  erected  at  the  present  day  without  the  use 
of  a  large  quantity  of  this  product.  Architectural  fayence,  of  high 
artistic  merit,  and  consisting  of  a  terra-cotta  body  covered  with  matt- 


PLATE   XVIII 


FIG.  1. — Roofing-tile  press  for  molding  interlocking  tile.     (After  H.  Ries, 
N.  Y.  State  Mus.,  Bull.  35,  p.  765,  1900.) 


FIG.  2. — Modeling  terra-cotta  objects.      (Photo  by  H.  Ries.) 

255 


KINDS  OF  CLAYS  257 

glaze  or  bright  enamel,  is  a  form  of  terra-cotta  now  made  by  several 
art  potteries  as  well  as  terra-cotta  works. 

In  the  manufacture  of  terra-cotta  the  clay  is  usually  ground  first 
in  a  dry  pan  (p.  219),  having  sometimes  been  previously  exposed  to 
the  weather,  partly  for  the  purpose  of  disintegrating  the  clay.  The 
ground-clays  are  often  tempered  in  a  wet  pan  (p.  220),  and  may  then  be 
subjected  to  still  further  mixing  in  a  pug-mill  of  either  vertical  or  hori- 
zontal type.  The  clay  issues  from  this  as  a  square  bar,  and  is  cut  up 
into  Lumps  which  are  piled  up  and  kept  covered  until  ready  for  use. 

Terra-cotta  is  always  formed  by  hand,  either  in  plaster  molds  or 
by  modeling.  The  former  method  is  employed  for  all  simple  forms, 
but  for  intricate  undercut  designs  it  is  necessary  to  model  the  pieces 
free-hand  (PI.  XVIII,  Fig.  2),  and  every  terra-cotta  factory  has  its  corps 
of  skilled  modelers  for  this  purpose.  In  making  a  mold  it  is  first  neces- 
sary to  make  a  plaster  model  around  which  the  mold  can  be  cast.  Small 
and  simple  designs  can  be  molded  in  one  piece,  but  larger  objects  or 
special  shapes  have  to  be  formed  in  several  pieces  which  are  joined 
together  when  set  in  the  building.  In  filling  a  plaster  mold  the  tem- 
pered clay  is  pushed  into  all  the  corners  and  crevices  and  spread  over 
the  entire  inner  surface  of  the  mold  to  a  depth  of  about  an  inch  and 
a  half,  after  which  the  sides  are  connected  by  clay  walls  or  partitions 
to  strengthen  the  piece.  The  mold  is  then  set  aside  for  several  hours 
in  order  to  permit  the  clay  to  shrink  sufficiently  to  allow  of  its  being 
removed  from  the  plaster  form.  Any  rough  or  uneven  edges  are  then 
usually  trimmed  off  with  a  knife. 

Terra-cotta  is  usually  dried  on  steam-heated  floors,  and  this  process 
must  be  carried  on  slowly  and  carefully  with  large  pieces.  For  large 
complex  pieces,  the  drying  may  even  be  retarded.  After  thorough 
air-drying  the  green  ware  is  taken  to  the  spraying-room,  where  the 
slip  which  is  to  form  the  surface  coating  is  sprayed  on  it,  thus  form- 
ing a  thin  layer  over  all  the  surface,  and  also  being  somewhat  absorbed 
by  the  body.  The  slip,  which  is  commonly  a  mixture  of  kaolin,  ball- 
clay,  quartz,  and  feldspar  (or  other  fluxes)  to  which  the  proper  color- 
ing ingredients  are  added,  forms  an  impervious  layer  on  the  surface 
of  the  terra-cotta,  and  also  produces  the  color  effect  on  the  ware.  It 
is  sometimes  of  such  composition  as  to  burn  to  a  dull  enamel.  Full- 
glazed  terra-cotta  is  but  little  made  in  the  United  States,  but  the 
demand  for  matt-glazed  or  semi-dull  glazed  terra-cotta  has  greatly 
increased  in  the  last  two  years.  This  effect  was  first  produced  by  sand- 
blasting a  full-glazed  surface,  but  proved  unsatisfactory,  and  at  present 
the  best  plants  are  covering  such  ware  with  a  regular  matt-glaze. 


258  CLAYS 

Terra-cotta  is  commonly  burned  in  circular  down-draft  kilns,  whose 
diameter  ranges  from  15  to  25  feet,  the  kilns  being  of  the  muffle  type. 
That  is  to  say,  they  have  a  double  wall  through  which  the  gases  of  com- 
bustion pass,  and  do  not  come  in  contact  with  the  ware,  which  becomes 
heated  by  radiation  from  the  walls  of  the  muffle.  The  different  pieces 
are  set  in  the  kiln  surrounded  by  a  framework  of  tiles  and  pipes  of  fire- 
clay (PL  XIX,  Fig.  1),  so  that  during  the  burning  no  object  has  to  bear 
any  weight  other  than  its  own.  The  total  shrinkage  in  drying  and 
burning  is  commonly  about  8  per  cent,  and  the  ware  is  never  burned 
to  vitrification.  Some  terra-cotta  manufacturers  burn  at  as  low  a 
cone  as  02,  but  the  majority  probably  reach  cones  6  or  8. 

Floor-tile 

Under  this  heading  are  included  tile  of  a  variety  of  shapes  and  colors 
which  are  used  for  flooring.  On  account  of  the  conditions  under  which 
they  are  used  they  should  possess  sufficient  hardness  to  resist  abrasive 
action,  sufficient  transverse  strength  to  resist  knocks,  and  sufficient 
density  to  prevent  excessive  absorption  of  water.  White  tiles  show 
little  or  no  absorption,  but  some  of  the  other  colors  soak  up  from  1  to 
5  per  cent  of  moisture,  or  perhaps  even  more.1 

Great  care  is  necessary  in  the  selection  of  raw  materials  for  floor- 
tile  as  the  clays  used  must  be  such  that  they  will  not  form  surface  cracks 
after  being  air-pressed.  The  clay  should  also  be  free  from  any  ten- 
dency to  warp  or  split  in  burning  and  furthermore  the  manufacturer 
must  aim  to  adjust  his  mixtures  for  facing  and  backing  in  case  they 
are  different.  Clays  used  for  floor-tile  should  also  be  as  free  from  soluble 
salts  as  those  used  for  the  manufacture  of  pressed  brick  or  terra-cotta, 
although,  as  pointed  out  by  Langenbeck,2  soluble  lime  salts  may  come 
from  the  coloring  materials  used.  Thus  the  manganese  and  umber 
used  for  chocolates,  brown  and  black,  are  seldom  free  from  gypsum. 

Purdy3  has  suggested  the  following  classification  of  floor-tiles: 

[  Vitreous       j  White  Colored    .  ™  i  r     • 

\  Prepared  facing  body  on  a 
Face-tile.  .  .  .  {  ,  .  . 

j  Porous  j  Clay  Colors 

f  Vitreous  j  White  Colored  SM  bodieg  formed 

1  esserse -j  .  .      , 

I  Encaustic  j  Clay  Colors  geometric  shapes. 

1  N.  J.  Geol.  Surv.,  Fin.  Kept,,  VI,  p.  287,  1904. 

2  Chemistry  of  Pottery,  p.   155. 

3  Trans.  Amer.  Cer.  Soc.,  VII,  p.  95,  1905. 


•8  I 


$3 

o|g 
•^   o  ^r 


10 

C    hC  r-5 


KINDS  OF  CLAYS  261 

Floor-tile  when  white  are  commonly  made  of  a  mixture  of  white- 
burning  clays,  flint,  and  feldspar.  Buff-colored  tiles  and  artificial  ones 
are  usually  made  from  fire-clays,  while  red  tiles  are  often  made  from 
a  red-burning  clay  or  shale.  A  certain  amount  of  flint  and  feldspar  is 
generally  added  to  the  clay  to  regulate  the  shrinkage  or  degree  of  vitri- 
fication in  burning. 

Floor-tiles  are  always  molded  by  the  dry-press  process  in  hand- 
potoer  machines,  the  raw  material  being  first  carefully  ground  and 
mixed. 

In  burning  tiles  they  are  placed  in  saggers  and  burned  in  down-draft 
kilns. 

The  face-tiles  include  the  plain  or  Alhambra  6X6  tile  strips  of  various 
sizes,  such  as  6X3  and  6X1J  used  as  body  tile,  and  are  most  generally 
made  with  a  prepared  facing  body  backed  by  a  common  body,  the 
latter  being  ground  in  a  dry  pan  to  a  16-mesh  powder. 

In  the  manufacture  of  these  plain  tiles  the  face  of  the  die  is  covered 
to  the  required  thickness  with  the  required  facing  body  and  the  rest 
of  the  die  filled  up  with  backing  clay,  after  which  the  pressure  is  applied. 

For  making  inlaid  tile  a  brass  cell  frame  of  the  same  depth  as  the 
facing  body  is  used,  and  consists  of  a  framework  of  brass  strips  arranged 
so  as  to  form  the  outline  of  the  colors  making  the  pattern.  The  frame* 
work  is  placed  in  the  mold  and  the  colored  clays  sifted  into  their  proper 
divisions.  This  is  done  by  using  a  sieve  so  perforated  as  to  expose  only 
certain  cells,  and  the  exposed  cells  being  filled  with  the  facing  mixture 
of  the  desired  color.  This  means,  of  course,  that  it  is  necessary  to 
use  as  many  sieves  as  there  are  colors  in  the  design.  The  cell  frame 
is  then  lifted  out  and  the  die  is  filled  with  a  clay  backing. 

In  making  tessera  the  body  is  solid,  namely,  made  entirely  from 
one  body  mixture.  The  vitreous  tesserae 1  are  porcelains,  so  com- 
pounded as  to  develop  the  greatest  toughness  or  resistance  to  wear  under 
feet  that  is  consistent  with  the  texture  of  the  body  and  the  brilliancy 
of  the  colors  demanded  by  the  trade. 

Encaustic  tesserae  tiles  have  for  their  base  buff-  and  red-burning 
clays.  Since  the  iron  in  these  is  mainly  present  as  free  oxide,  it  is  im- 
possible to  burn  such  tiles  to  vitrification  without  destroying  the  color. 

Wall-tile 

These  are  quite  different  from  floor-tile  in  the  character  of  body  and 
style  and  decoration.  The  body  is  made  of  white-burning  clay  and  is 

'Purdy,  op.  cit.,  p.  101. 


282  CLAYS 

not   burned  to  vitrification,  but  on  the   contrary  is   usually  just  hard 
enough  to  resist  scratching  with  a  knife.     It  is  therefore  very  porous. 

Wall-tile  are  molded  in  dry-press  machines  and  burned  first  in 
saggers  in  a  biscuit-kiln.  They  are  then  glazed  and  fired  in  a  muffle- 
kiln  at  a  much  lower  temperature.  Many  different  shades,  colors,  and 
styles  of  decoration  are  now  produced.  In  some  cases  the  decoration 
is  applied  by  a  relief  design  impressed  on  the  surface  of  the  clay  during 
molding,  in  others  different  colored  glazes  are  used,  or  a  considerable 
variation  can  be  obtained  in  the  shades  of  one  color  by  varying  the 
thickness  of  the  glaze  over  different  parts  of  the  tile.  Print-work  and 
hand-painting  also  are  employed  at  times  to  ornament  the  ware. 

Pottery 

Classification. — Under  the  term  of  pottery  there  is  included  a  great 
series  of  products  for  ornamental  or  domestic  use,  ranging  from  the 
common  red  earthenware  flower-pot  to  the  highly  artistic  and  deli- 
cate porcelain  vase.  The  different  kinds  may  be  defined  as  follows: 

Common  earthenware,  made  from  the  lower  grades  of  plastic  clays, 
and  having  a  porous  body,  usually  of  red  but  sometimes  cream  color, 
and  as  a  rule  not  glazed.  Decoration  is  given  to  it  by  relief  designs, 
produced  during  the  molding  process,  or  more  rarely  by  painting  or 
glazing. 

Yellow  or  Rockingham  ware,  covering  wares  made  of  semi-fire  clays 
or  fire-clays,  and  having  a  porous  buff-colored  body,  which  is  covered 
with  a  glaze. 

Majolica  and  Fayence. — Both  these  terms  are  rather  loosely  used, 
but  a  definition  recently  suggested  by  S.  G.  Burt l  gives  fayence  as 
pottery  in  which  the  colored  clay  body  is  covered  with  a  clear  glaze, 
and  majolica  as  pottery  in  which  the  colored  clay  body  is  concealed 
with  an  opaque  enamel. 

Stoneware,  made  of  vitrifiable  clays,  often  of  semi-refractory  char- 
acter, and  having  a  vitrified  body,  often  of  bluish  color  but  never  white. 
The  surface  is  glazed. 

White  ware,  including  those  products  having  a  white  or  nearly  white 
porous  body,  usually  covered  with  a  glaze.  There  are  several  trade 
varieties  of  this  known  as  C.  C.  ware,  white  granite  ware  or  ironstone 
china,  semi-vitreous  ware,  semi-porcelain,  and  china.  Some  of  these 
differ  at  times  in  name  only.  Theoretically  they  differ  in  the  white- 
ness and  degree  of  vitrification  of  the  body. 

1  Trans.  Amer.  Cer.  Soc.,  VI,  p.  109,  1904. 


KINDS  OF  CLAYS  263 

The  technology  of  the  lower  grades  of  pottery  is  comparatively 
simple,  but  for  the  manufacture  of  white  ware  or  porcelain  the  success- 
ful completion  of  the  product  calls  for  skill,  intelligence,  and  good  mate- 
rials. 

There  was  a  time  when  whiteware  mixtures  and  glazes  of  the  proper 
quality  could  be  obtained  only  after  long  and  tedious  experimenting 
and  the  expenditure  of  much  time  and  money,  and  while  many  potters 
are  still  groping  in  the  dark,  the  day  of  this  cut-and-try  method  can 
be  said  to  have  passed.  Modern  ceramic  technology  has  worked  wonders 
and  a  knowledge  of  it  proves  invaluable  to  the  progressive  potter  in 
aiding  him  to  work  out  the  proper  combinations  of  body  and  glaze. 
It  enables  him  to  adjust  them  if  they  do  not  agree,  or  to  find  out  often 
in  a  comparatively  short  time  where  the  trouble  lies  when  failures 
occur. 

To  take  advantage  of  the  facts  and  principles  of  ceramic  technology 
does  not  so  much  require  a  very  profound  knowledge  of  chemistry  as 
a  good  technical  training,  and  the  potter  who  seeks  and  grasps  these 
ceramic  principles  will  advance  rapidly,  while,  on  the  other  hand,  he 
who  rejects  them  and  carefully  guards  some  elementary  facts  as  imagin- 
ary secrets  of  great  value  does  himself  a  positive  injury.  Freedom 
of  discussion  has  proven  an  invaluable  aid  in  other  technical  branches, 
and  there  is  no  apparent  reason  why  it  should  not  do  the  same  for  the 
pottery  industry.  The  subject  of  ceramic  technology  in  America  has 
been  behind  that  of  Europe  for  many  years,  although  it  is  now  coming 
forward  with  rapid  strides.  The  annual  meetings  of  the  American 
Ceramic  Society  form  a  center  where  clay-workers  can  gather,  and  both 
give  and  receive  information  without  the  necessity  of  disclosing  any 
business  secrets.  Indeed,  so  successful  have  these  meetings  become 
that  the  printed  transaction  of  the  society  form  a  most  valuable  series 
of  works  dealing  in  a  technical  and  scientific  way  with  clays  and  clay- 
products. 

In  addition  to  this  ceramic  schools  have  been  established  in  several 
States,  and  provision  thereby  made  for  instruction  in  modern  ceramic 
technology  and  the  investigation  of  allied  subjects. 

Manufacture  of  Pottery 

In  making  pottery  there  are  certain  steps  that  are  common  to  all 
grades  of  ware,  but  the  care  of  preparation  and  the  number  of  steps 
are  increased  in  the  manufacture  of  the  higher  grades. 

The  different  steps  may  be  grouped  as  follows: 


264 


CLAYS 


Preparation 


Tempering 


Molding 


Weathering 

Grinding 

Washing  by  sedimentation 

Blunging  and  filter-pressing 
(  Ball-mills 
f  Chaser-mills 
J  Pug-mills 

Hand-wedging 

Wedging-tables 

Turning 

Jollying  or  jiggering 

Pressing 

Casting 
Drying 

Biscuit-burning 
Dipping 
Glost-burning 
Decorating 

Preparation 

Weathering  and  grinding. — For  the  commoner  grades  of  pottery, 
such  as  red  earthenware  and  often  even  for  stoneware,  the  clay  or  shale 
are  used  as  they  come  from  the  bank  or  mine. 

Weathering  is  sometimes  resorted  to  in  order  to  soften  the  clay 
and  disintegrate  it,  so  that  it  can  be  more  readily  washed,  or  to  facili- 
tate mixing  it  when  washing  is  omitted.  Shales  are  sometimes  crushed 
without  being  weathered. 

Washing. — For  the  higher  grades,  such  as  white  ware  and  porce- 
lains, the  raw  clay  is  washed  in  order  to  free  it  from  sand  or  other  heavy 
and  coarse  impurities. 

Blunging  and  filter-pressing. — The  Hunger  consists  of  a  circular 
vat  in  which  there  revolves  two  arms  with  stirring-rods  attached.  In 
this  the  clay  mixture  and  water  become  thoroughly  stirred  and  mixed, 
after  which  the  contents  of  the  blunger  are  run  through  a  fine  screen 
of  100  or  150  meshes  to  the  inch  into  a  cistern,  from  which  it  is  pumped 
to  the  filter-press  (p.  214  and  PL  X,  Fig.  2).  The  pressed  clay  then 
goes  to  a  pug-mill  after  which  it  is  further  wedged  before  use.  This 
process  of  preparation  is  now  used  by  nearly  all  potteries  of  any  size, 
except  those  manufacturing  common  earthenware.  For  glazed  earthen- 
ware bodies  it  means  simply  washing,  blunging,  screening,  and  filter- 


KINDS  OF  CLAYS  265 

pressing  the  clay  body,  but  for  white-ware  bodies  a  somewhat  more 
elaborate  system  of  treatment  is  necessary,  since  these  carry  kaolin, 
ball-clay,  quartz,  and  feldspar,  which  must  be  intimately  mixed. 

Ball-mills. — Ball-mills  are  employed  in  the  preparation  of  clay  in 
the  manufacture  of  some  of  the  finer  grades  of  wares,  where  fine  grinding 
and  intimate  mixture  of  ingredients  is  especially  important.  They  con- 
sist of  a  hollow  cylinder  that  rotates  on  a  horizontal  axle  and  into  which 
the  "clay  to  be  ground  is  admitted  through  an  opening  at  one  side  or 
end.  The  machine  is  charged  with  the  clay  and  balls  (which  fill  about 
one  third  of  the  volume  of  the  cylinder),  the  latter  being  of  porcelain 
or  water-worn  Iceland-flint  pebbles.  The  material  is  pulverized  by 
abrasion  or  rubbing  friction  between  these  balls  as  they  are  caused 
to  move  upon  each  other  by  the  rotation  of  the  cylinder.  There  are 
two  principal  types  of  ball-mills  which  may  be  designated  as  the  inter- 
mittent and  the  continuous.  The  former  are  those  which  are  run  with 
a  given  charge  until  the  requisite  degree  of  fineness  is  attained,  when 
this  is  removed  and  another  charge  put  in.  This  class  of  apparatus 
may  be  used  to  grind  either  in  the  dry  or  wet  state.  The  latter  or  con- 
tinuous class  includes  the  more  improved  types  of  ball-mills  for  turning 
out  a  large  product  of  very  finely  dry-ground  materials.  They  are 
so  arranged  that  the  raw  ingredients  are  fed  in  at  one  end  of  the  rotating 
cylinder  and  gradually  work  their  way  towards  the  other  end,  becoming 
finer  and  finer  until  they  are  discharged  in  the  desired  state  of  com> 
minution,  when  the  opposite  end  of  the  drum  is  reached.  The  continu- 
ous ball-mill  is  in  use  very  little,  if  at  all,  in  this  country,  but  is  rapidly 
coming  into  use  in  Germany.  The  periodic  mill  is  used  to  some  extent 
by  potteries  in  this  country. 

Tempering 

Chaser-mills,  which  may  be  regarded  as  a  form  of  wet  pan,  are  some- 
times used  at  the  stoneware  factories.  They  consist  of  a  circular  iron 
pan  in  which  there  revolves  a  frame  bearing  two  narrow  iron  wheels* 
30  to  36  inches  in  diameter.  As  this  frame  revolves  the  wheels,  by 
means  of  a  gearing,  travel  around  the  pan  in  a  spiral  path.  The  clay 
and  water  are  placed  in  the  pan  and  the  action  of  the  wheels  grinds 
a.id  cuts  it  up,  the  tempering  taking  from  one  to  two  hours.  The  action 
of  such  a  machine  is  quite  thorough,  but  considerable  power  is  required 
to  operate  it.  Their  use  has  been  largely  discontinued  since  the  intro- 
duction of  the  blunger  and  filter-press. 

Pug-mills  and  hand- wedging. — The  washed  clays  or  mixtures  of 
clays  as  they  come  from  the  filter-press  are  tempered  in  a  vertical  or 


266  CLAYS 

horizontal  pug-mill,  which  is  similar  in  its  action  to  that  described 
under  Brick  (p.  220).  This  is  then  followed  by  hand-wedging  in  order 
to  render  the  clay  perfectly  homogeneous  and  free  from  air-bubbles. 
This  latter  operation  consists  in  taking  a  large  lump  of  the  pugged  clay, 
cutting  it  in  two,  bringing  the  two  parts  together  with  force,  and  then 
kneading  the  reunited  lumps,  this  treatment  being  repeated  a  num- 
ber of  times. 

Wedging-tables. — Kneading-tables  are  used  at  some  factories  for 
working  the  clay  by  machine  instead  of  wedging  it  by  hand.  Although 
much  used  abroad,  then-  introduction  into  this  country  has  been  rather 
restricted.  The  machine  consists  of  a  circular  table  about  6  feet  in 
diameter,  the  upper  surface  of  which  slopes  outward.  On  this  are  two 
conical  rolls,  20  to  30  inches  in  diameter  and  about  8  inches  wide.  These 
rolls  have  corrugated  rims,  and  are  attached  to  opposite  ends  of  a  hori- 
zontal axis,  having  a  slight  vertical  play.  The  clay  is  laid  on  the  table, 
and  as  the  rolls  travel  around  on  it  the  clay  is  spread  out  into  a  broad 
band.  A  second  axle  carries  two  other  pah's  of  rolls  of  the  same  shape 
but  smaller  size,  which  travel  around  in  a  horizontal  plane.  These 
rolls  press  the  band  of  clay  together  again.  In  this  way  the  clay  is 
subjected  to  alternating  vertical  and  lateral  pressure  and  all  air-spaces 
are  thus  closed.  The  rolls  make  10  to  12  revolutions  per  minute,  and 
the  machine  kneads  2  to  3  charges  of  700  pounds  per  hour. 

Molding 

After  the  clay  has  been  properly  tempered,  the  next  step  in  the 
process  of  manufacture  is  molding.  As  indicated  above,  this  is  done 
in  four  different  ways,  the  clay  having  first  been  thoroughly  kneaded, 
usually  by  hand,  in  order  to  insure  its  complete  homogeneity  and  free- 
dom from  all  air-bubbles. 

Turning  is  done  by  the  potter  taking  a  lump  of  clay  and  placing 
it  on  a  rapidly  revolving  horizontal  disk  and  gradually  working  it  up 
into  the  desired  form  (PI.  XXI).  After  being  turned  the  object  is  then 
detached  from  the  wheel  by  running  a  thin  wire  underneath  it.  Only 
articles  with  a  circular  cross-section  and  thick  walls  can  be  formed  in 
this  manner,  since  they  have  to  hold  their  shape  under  their  own  weight. 
Turning  represents  the  earliest  methods  of  the  potter,  and  is  much 
used  still  at  small  factories,  but  in  the  larger  ones  it  has  been  mostly 
superseded  by  the  next  process. 

Jollying  or  jiggering  is  a  more  rapid  method  than  turning,  and  the 
clay  for  this  purpose  is  tempered  to  a  softer  consistency.  The  jolly 


PLATE    XX 


Bergstrom  &  Bass  Tile-press. 


267 


KINDS  OF  CLAYS  269 

is  a  wheel  fitted  with  a  hollow  head  to  receive  the  plaster  mold, 
the  interior  of  which  is  the  same  shape  as  the  outside  of  the  object 
to  be  molded.  A  lump  of  clay  is  placed  in  the  revolving  mold  and 
shaped  into  the  proper  form,  first  by  means  of  the  fingers  and  lastly 
by  means  of  a  template  or  so-called  "shoe"  attached  to  a  pull-down 
arm,  which  is  brought  down  into  the  mold.  Cups,  jars,  jugs,  and  the 
larger  flower-pots  are  molded  in  this  manner.  A  modification  of  this 
method  termed  "  pressing  "  is  used  for  the  smaller  sizes  of  flower-pots. 
This  consists  of  a  revolving  steel  mold,  with  a  steel  plunger  of  the  shape 
and  size  of  the  interior  of  the  pot.  The  tempered  clay  is  first  put  through 
a  plunger-machine,  from  which  it  issues  in  the  form  of  columns,  which 
are  cut  up  by  wires  into  a  number  of  pieces,  each  containing  just  enough 
clay  for  making  a  pot  of  the  desired  size.  These  lumps  of  clay  are 
then  placed  one  at  a  time  in  the  mold,  and  the  latter  raised  by  means 
of  a  lever,  until  the  plungers  fit  into  it,  thus  pressing  the  clay  into  the 
mold.  The  bottom  of  the  mold  is  movable,  so  that  as  the  mold  is  lowered 
the  bottom  rises  and  pushes  out  the  pot.  Such  machines  have  a  large 
capacity,  and  are  now  used  at  most  flower-pot  factories.1 

A  modification  of  jollying,  used  for  making  plates  and  saucers,  con- 
sists in  having  a  plaster  mold,  the  surface  of  which  has  the  same  shape 
as  the  interior  or  upper  surface  of  the  plate  to  be  formed.  The  potter's 
assistant  takes  a  piece  of  clay  of  the  desired  size,  and  pounds  it  to  a 
flat  cake,  called  a  "bat,"  which  is  laid  on  the  mold;  he  then  shapes 
the  other  side  or  bottom  of  the  plate  by  pressing  a  wooden  template 
of  the  proper  profile  against  it  as  it  revolves. 

Pressing. — Ewers  and  vessels  of  oval  or  elliptical  section  are  usu- 
ally made  by  means  of  sectional  molds,  consisting  of  two  or  three  pieces, 
the  inner  surface  of  which  conforms  to  the  outer  surface  of  the  object 
to  be  molded.  A  slab  of  clay  is  laid  in  each  section  and  carefully  pressed 
in,  the  mold  put  together,  and  all  seams  smoothed  with  a  wet  sponge. 
After  drying  for  a  few  hours  the  parts  of  the  mold  are  lifted  off. 
Clocks,  lamps,  water-pitchers,  and  similar  articles  are  made  in  this 
manner. 

Casting. — This  consists  in  pouring  a  clay-slip  into  a  plaster  mold 
which  absorbs  some  of  the  water,  and  causes  a  thin  layer  of  the  clay 
to  adhere  to  the  interior  surface  of  the  mold.  In  order  to  produce  a 
slip  with  less  water  some  alkaline  salt  is  added  to  the  mixture.  When 
the  layer  on  the  inner  surface  of  the  mold  is  sufficiently  thick,  the  mold 
is  inverted  and  the  remaining  slip  is  poured  out,  the  mold  being  removed 

1  Fire-clay  crucibles  are  sometimes  molded  by  this  method. 


270  CLAYS 

in  a  few  hours.  This  method  is  extensively  used  in  making  thin  por- 
celain ornaments,  as  well  as  many  white-ware  objects.  It  is  also  employed 
for  making  belleek. 

The  forming  of  pottery  by  casting  is  much  more  extensively  done  in 
Europe  than  in  the  United  States. 

Drying 

This,  of  necessity,  often  has  to  proceed  rather  slowly,  especially  if 
the  ware  is  of  complicated  shape.  The  ware  is  usually  dried  first  in 
an  open  room,  and  then  removed  to  the  heated  green- ware  dry-room. 

Subsequent  steps 

Up  to  this  point,  the  method  of  treatment  has  been  much  the  same 
except  for  the  blunging  of  white  ware  or  porcelain  mixtures.  From 
the  drying  stage  on,  the  methods  of  treatment  of  the  different  kinds 
of  ware  diverge  somewhat. 

Common  red  earthenware,  such  as  flower-pots,  is  usually  burned 
at  a  low  heat,  often  not  above  the  melting-point  of  cone  010,  and  the 
kilns  used  are  generally  rectangular  or  circular  up-draft  ones.  The 
ware  after  burning  is  quite  porous  and  not  steel-hard. 

If  to  be  decorated  this  can  be  done  by  incised  designs,  the  appli- 
cation of  relief  decoration,  or  by  covering  it  with  a  glaze  of  easy  fusi- 
bility. 

Yellow  and  Rockingham  ware. — In  making  this  the  clay  is  first 
burned  to  develop  the  body,  after  which  it  is  glazed  and  then  fired 
a  second  time  to  develop  the  glaze,  the  process  in  this  respect  being 
similar  to  that  employed  for  white  ware,  and  the  ware  being  placed  in 
saggers  to  protect  it  from  the  flames  and  dirt.  The  glazes  are  artificial 
mixtures  which  melt  to  a  glass  at  a  lower  temperature  than  that  re- 
quired to  burn  the  body. 

Stoneware. — In  this  class  of  product  the  body  and  glaze  are  de- 
veloped together,  so  that  after  drying  the  objects  are  ready  to  have  the 
glaze  applied.  A  type  sometimes  used  is  some  form  of  natural  glaze 
or  slip-clay  (see  p.  193),  which  melts  to  a  brown  glass  at  a  temperature 
at  which  the  body  of  the  ware  is  nearly  vitrified. 

For  application  the  slip-clay  is  mixed  with  water  to  a  creamy  con- 
sistency and  the  ware  dipped  in  it.  Although  slip-clays  have  been 
found  at  a  number  of  localities  in  the  United  States,  that  obtained 
from  Albany,  N.  Y.,  continues  to  be  the  most  satisfactory  and  is  shipped 
all  over  the  country.  The  amount  of  slip-clay  required  even  by  a 


KINDS  OF  CLAYS  271 

factory  of  moderate  size  is  not  very  large,  so  that  the  annual  domestic 
consumption  of  this  kind  of  clay  is  limited. 

Salt-glazing  represents  the  simplest  form  of  glazing  a  ware,  and  is 
applied  more  often  to  sewer-pipe  than  stoneware.  When  the  wares 
are  to  be  salt-glazed  they  are  placed  in  the  kiln,  unprotected  from  the 
flames.  As  soon  as  the  kiln  has  reached  its  highest  temperature,  the 
salt  is  put  in  the  fireplaces,  one  or  two  shovelsfull  at  a  time,  at  regular 
intervals,  so  that  the  addition  of  the  salt  may  extend  over  several  hours. 
When  the  salt  is  placed  in  the  fires  the  heat  volatilizes  it,  and  the  vapors 
in  passing  up  through  the  kiln  unite  with  the  clay,  forming  a  glaze  on 
the  surface  of  the  ware.  Many  clays  are  capable  of  taking  a  good  salt- 
glaze,  but  some  take  a  poor  one,  and  others  do  not  glaze  at  all. 

From  experiments  made  by  L.  E.  Barringer  l  it  seems  that  a  clay 
may  be  either  too  aluminous  or  too  siliceous  to  be  successfully  salt- 
glazed,  but  that,  if  the  process  of  salt-glazing  is  properly  carried  out, 
clays  in  which  the  proportion  of  silica  to  alumina  is  more  than  4.6  to 
1  and  less  than  12.5  to  1  are  capable  of  receiving  a  glaze.  The  degree 
of  fineness  of  the  free  silica  in  the  clay  makes  little  difference.  The 
finer  the  sand  the  lighter  the  color  of  the  glaze. 

Barringer  also  found  that,  contrary  to  what  was  usually  supposed, 
a  considerable  quantity  of  soluble  salts,  as  much  as  3  per  cent,  can  be 
present  in  a  clay  without  seriously  interfering  with  the  salt-glazing 
when  conducted  at  cone  8. 

Bristol  glazes,  representing  a  third  type,  are  an  artificial  mixture 
of  fluxes,  kaolin,  ball-clays,  and  flint.  They  can  be  produced  in  a 
variety  of  colors,  and  white,  due  to  zinc  or  tin,  is  a  common  one.  This 
is  the  type  of  glazing  generally  used  on  stoneware. 

The  burning  of  stoneware  is  carried  out  in  up-draft  or  down-draft 
kilns,  and  the  cone  reached  varies  in  different  localities,  but  where 
fire-clays  or  semi-fire  clays  are  employed  it  ranges  probably  from 
6  to  8. 

White  ware  and  porcelain. — Both  of  these  are  made  from  artificial 
mixtures,  consisting  of  kaolin,  ba,ll-clay,  quartz,  and  feldspar,  and 
the  materials  used  are  selected  with  a  view  to  their  white-burning 
qualities. 

The  kaolin  supplies  white  color  and  refractoriness  but  is  low  in  plas- 
ticity, and  to  supply  this  deficiency  ball-clay  is  added.  Quartz  serves 
to  diminish  the  shrinkage,  and  feldspar  or  calcined  bones  as  a  flux. 

Porcelain  in  which  spar  is  the  flux  is  termed  hard,  feldspar  or  true 

1  Trans.  Amer.  Cer.  Soc.,  IV,  p.  223. 


272  CLAYS 

porcelain,  and  shows  a  bluish-white  color  by  transmitted  lights,  while 
that  which  is  fluxed  in  part  by  calcined  bones  or  lime  phosphate  is 
termed  bone  china  and  shows  a  yellowish  color  by  transmitted 
light. 

The  proportions  in  which  these  several  substances  are  used  are 
commonly  kept  secret  by  the  potter,  but  enough  has  been  published  to 
show  the  general  mixtures. 

In  the  molding  of  white  and  porcelain  wares  jiggering  and  pressing 
are  extensively  employed,  and  the  burning  is  done  in  much  the  same 
manner  as  in  yellow  wrare. 

Saggers,  which  are  oval  or  cylindrical  receptacles  made  of  fire-clay 
with  a  flat  bottom,  about  20  inches  in  diameter  and  a  height  usually 
of  about  8  inches,  are  used  for  protecting  the  ware  in  the  kilns. 

The  saggers  are  filled  with  unburned  ware  and  set  one  on  top  of 
the  other  (PI.  XIX,  Fig.  2),  so  that  the  bottom  of  one  forms  a  cover 
for  the  one  below  it,  the  joint  between  the  two  being  closed  by  a  strip 
of  "  wad  "-clay.  The  use  of  these  saggers  is  to  protect  the  ware  from 
the  smoke,  gases,  and  ashes  of  the  kiln-fire.  The  chief  requisite  of  a 
sagger-clay  is  that  it  shall  stand  more  heat  than  the  ware  placed  in  it, 
and  repeated  firing  and  cooling,  as  well  as  handling  without  breaking. 
Saggers  are  generally  made  from  a  plastic,  refractory  clay,  with  the 
maximum  admixture  of  grog,  i.e.,  ground  old  saggers,  broken  fire-brick, 
etc.  The  kilns  are  usually  of  the  circular  up-draft  type  having  a  diam- 
eter of  from  10  to  18  feet.  Down-draft  kilns  are  but  little  used  for 
burning  white  ware  in  the  United  States,  although  in  Europe  the  down- 
draft  method  of  burning  has  superseded  the  up-draft.  The  temperature 
reached  in  burning  varies.  White  ware  is  commonly  burned  at  from 
cones  8  to  9,  while  the  porcelain  may  be  fired  as  high  as  cones  12  to  16. 
Since  the  color  of  ferrous  iron  is  less  noticeable  than  ferric  iron  the 
fires  should  be  reducing  during  at  least  the  last  part  of  the  firing,  and 
the  kiln  is  then  cooled  down  as  rapidly  as  possible  to  prevent  the  oxi- 
dation of  whatever  iron  may  be  in  the  clay. 

For  all  pottery  ware,  except  hard  or  feldspar  porcelains,  the  body 
is  first  burned  in  the  biscuit-kiln,  then  glazed  and  burned  a  second  time 
in  the  glost-kiln.  For  white  ware  the  biscuit-burn  is  done  at  perhaps 
cones  8  to  9,  while  the  glost-burn  at  about  2  to  6.  For  yellow  and  Rock- 
ingham  ware,  fayence  and  majolica,  the  biscuit-burn  ranges  between 
cones  2  to  8,  while  the  glost  is  from  cones  07  to  03.  For  porcelain  the 
biscuit-burn  is  about  cone  2,  while  the  glost-burn  is  at  a  higher  heat, 
and  in  this  country  ranges  probably  from  cones  11  to  13. 

The  glazes  for  white  ware  and  porcelain  are  complex  compounds 


PLATE   XXI 


Views  illustrating  the  process  of  turning  jars.     (Photo  by  H.  H.  Hindshaw 
Md.  Geol.  Surv.,  IV,  p.  358,  1902.) 

273 


KINDS  OF  CLAYS  275 

of  an  artificial  character.  They  consist  of  a  mixture  of  acids  and  bases 
combined  according  to  a  definite  formula,  in  such  proportions  that  they 
will  melt  to  a  glass  at  the  temperature  reached  in  burning.  A  glaze 
thus  produced  must  furthermore  agree  with  the  body  in  its  shrinkage 
and  coefficient  of  expansion,  in  order  to  prevent  various  defects,  such 
as  crazing,  shivering,  peeling,  etc.  A  discussion  of  the  composition  and 
methods  of  calculating  glaze  formulas  hardly  lies  within  the  province 
of  this  work,  and  those  wishing  to  become  acquainted  with  this  sub- 
ject are  referred  to  a  most  excellent  little  manual  of  Ceramic  Calcula- 
tions issued  by  the  American  Ceramic  Society.1 

The  glazes  used  on  white  ware  are  usually  fritted  first.  That  is, 
the  ingredients  of  the  glaze  after  mixing  are  melted  either  in  a  frit- 
kiln  or  a  sagger,  broken  up  and  ground  wet,  together  with  certain  added 
materials.  This  glaze  mixture  is  then  of  a  cream-like  consistency  and 
the  biscuit  ware  is  dipped  into  it  (PL  XXIIj.  In  the  glost-kiln  this 
thin  coating  of  glaze  melts  to  a  glassy  layer  and  covers  the  body  en- 
tirely. White-ware  glazes  commonly  owe  their  easy  fusibility  to  borax 
and  lead,  while  those  used  on  porcelain  contain  no  lead,  and  require 
a  higher  heat  for  maturing. 

White  ware  and  porcelain  are  often  elaborately  decorated,  either 
under  or  over  the  glaze,  but  the  form  of  decoration  most  often  seen 
is  print-work.  This  is  done  by  printing  a  copper-plate  design  on  special 
paper,  and  applying  this  to  the  surface  of  the  ware.  After  being  allowed 
to  stand  for  a  few  hours  the  paper  is  washed  off,  but  the  ink  cf  the 
design  is  retained  on  the  surface  of  the  ware.  The  colors  are  then  fixed 
by  firing  in  a  muffle-kiln  at  a  dull-red  heat.  The  print-work  is  some- 
times " filled  in"  and  elaborated  by  brush-work,  or,  on  better  grades 
of  ware,  the  entire  design  may  be  hand-painted.  The  more  delicate 
colors  as  well  as  gold  have  to  be  applied  over  the  glaze  as  they  are  de- 
stroyed by  hard-firing.  With  chromolithography  a  soft  and  orna- 
mental multicolored  design  can  be  produced  at  one  operation,  but  it 
is  but  little  used  in  this  country,  although  productive  of  beautiful 
effects. 

Electrical  porcelain. — This  forms  a  separate  branch  of  the  clay- 
working  industry.  These  insulating  materials  are  made  of  a  mixture 
of  white-burning  clays,  feldspar,  and  flint,  and  molded  by  the  dry- 
press  process.  It  is  necessary  to  burn  them  to  vitrification,  and  none 
are  probably  burned  below  cone  10  and  some  at  cone  12.  They  are 
usually  glazed  in  one  burning. 

1  Purchasable  for  $1.00  from  Ed.  Orton,  Jr.,  Sec'y,  Columbus,  Ohio. 


276  CLAYS 

Sanitary  ware  is  made  sometimes  from  the  same  clay  bodies  as  white 
ware,  but  the  body  is  usually  vitrified  or  nearly  so,  and  is  glazed.  The 
ware  is  formed  by  hand  in  plaster  molds,  and  great  care  has  to  be  exer- 
cised in  drying  and  burning. 

Bathtubs  and  washtubs. — These  are  commonly  made  from  buff- 
burning  clays,  such  as  are  used  in  terra-cotta  manufacture,  and  covered 
with  both  a  white  slip  and  a  glaze.  The  lining  is  usually  vitrified,  but 
not  the  body,  and  they  are  termed  porcelain  lined.  The  pressing,  drying, 
and  burning  of  such  a  large  object  as  a  bathtub  requires  much  care 
and  time.  The  pressing  is  done  by  hand  in  large  plaster  molds,  and 
the  wares  are  burned  commonly  at  from  cones  9  to  10,  or  perhaps  slightly 
higher.  A  finished  bathtub  may  weigh  as  much  as  1100  pounds. 


\ 


CHAPTER  VI 
DISTRIBUTION   OF  CLAY  IN  THE   UNITED  STATES 

ALABAMA — LOUISIANA 

Introduction. — In  this  chapter  and  the  two  following  ones  it  is 
proposed  to  describe  briefly  the  occurrence,  properties,  and  uses  1  of  the 
clays  found  in  the  different  States.  While  it  is  thought  that  the  more 
important  facts  are  grouped  here,  still  there  may  be  some  who  wish 
to  obtain  additional  details,  which  they  can  do  by  looking  up  the  refer- 
ences given  at  the  end  of  the  discussion  of  each  State. 

A  grouping  of  the  clays  according  to  geologic  formations  has  been 
adopted  partly  because  the  subject  is  treated  mainly  from  the  stand- 
point of  the- economic  geologist,  and  partly  because  it  admits  of  greater 
uniformity  in  mode  of  presentation.  For  the  benefit  of  those  who  would 
prefer  a  grouping  by  kinds,  the  index  has  been  made  as  complete  as 
possible,  in  order  to  enable  them  to  find  .he  data  for  which  they  are 
searching. 

Statistics  of  Production. — Doubtless  few  people  realize  the  im- 
portance of  the  clay-working  industry  in  the  United  States,  and  yet 
this  is  not  so  surprising,  since  clay  has  less  popular  attraction  than 
many  other  mineral  products,  such  as  gold,  silver,  etc.  A  casual 
glance,  however,  at  the  annual  figures  of  production  will  probably 
speedily  convince  one  that  clay  is  to  be  classed  among  the  fore- 
most mineral  products  of  the  country,  being  outranked  only  by  coal 
and  iron. 

The  statistics  of  production  for  1904,  as  published  by  the  United 
States  Geological  Survey,  are  given  on  p.  278. 

1  This  refers  to  their  use  for  the  manufacture  of  clay-products. 

277 


278  CLAYS 

VALUE  OF  CLAY-PRODUCTS  OF  THE  UNITED  STATES  IN  1904 

P-duct.  Value. 

Common  brick $51,768,558               39 . 51 

Vitrified  paving-brick 7,557,425  5.77 

Front  brick 5,560,131  4 . 24 

Fancy  or  ornamental  brick.  .  . 845,630  .65 

Drain-tile 5,348,555  4.08 

Sewer-pipe 9,187,423  7.01 

Architectural  terra-cotta 4,107,473  3 . 14 

Fireproofing 2,502,603  1 . 91 

Hollow  blocks 1,126,498  .86 

Tile,  not  drain 3,023,428  2.31 

Fire-brick 11,167,972  8.52 

Miscellaneous 3,669,282  2 . 80 

Red  earthenware 756,625  . 58 

Stoneware 3,41 1 ,025  2 . 60 

Yellow  and  Rockingham  ware 290,819  .22 

C.  C.  ware 854,389  . 65 

White  granite  and  semi-porcelain 10,836,117  8.27 

China 1,583,513  1 . 21 

Bone  china,  delft,  and  belleek 162,500  . 12 

Sanitary  ware 3,585,375  2.74 

Porcelain  electrical  supplies 1,431,452  1 .09 

Miscellaneous  pottery. 2,246,455  1.72 


Total $131,023,248  100.00 

CLAY  MIXED  AND  SOLD  IN  THE  UNITED  STATES  IN  1904 

Kind.  Value. 

Kaolin.  . $304,582 

Paper 276,381 

Slip 11,942 

Ball 142,028 

Fire 1,306  053 

Stoneware 83,904 

Miscellaneous.  .               195,272 


Total $2.320  162 

Alabama 

The  clay-deposits  of  this  State   are  distributed  over  a  wide   range 
of  geologic  formations,  whose  characters  are  briefly  referred  to  below. 

Archaean  and  Algonkian 

The  rocks  of  this  age,  which  underlie  a  roughly  triangular  area  of 
the  eastern  part  of  the  State,  consist  of  granites,  gneisses,  and  schists, 


PLATE    XXII 


Dipping  biscuit  ware  into  the  glazing-tubs.     (Photo  by  H.  Ries.) 


279 


DISTRIBUTION   OF  CLAY  IN  THE  UNITED  STATES  281 

all  of  which  have,  by  surface  decay,  furnished  a  residual  clay,  usually 
of  ferruginous  character.  In  the  schist  areas,  however,  there  are  not 
a  few  pegmatite  veins,  whose  decomposition  has  resulted  in  the  forma- 
tion of  kaolin.  Such  occurrences  are  found  near  Milner,  Pinetucky, 
and  Micaville,  Randolph  County,  and  Stone  Hill  in  Cleburne  County, 
but  they  are  all  undeveloped,  owing  to  lack  of  railroad  facilities.  The 
Alabama  kaolins  in  their  crude  condition  are  rather  siliceous,  highly 
refractory,  and  burn  to  a  very  white  color. 

Cambrian  and  Silurian 

The  clays  obtained  from  these  formations  are  either  residual  deposits 
or  are  concentrates  from  these,  which  have  been  carried  by  surface- 
waters  down  into  sinks  and  other  depressions.  While  the  Silurian  rocks 
contain  some  shaly  members  they  are  not,  so  far  as  known,  used  for 
brickmaking,  but  the  residual  clays  which  are  usually  impure  are  ex- 
tensively employed  for  this  purpose.  At  certain  localities,  such  as  at 
Gadsden,  Kymulga,  Peaceburgh,  and  Oaxanna,  white  clays  occur  sur- 
rounded by  the  impure  ones,  and  those  found  in  Cherokee  County  have 
been  used  for  fire-brick  manufacture. 

Lower  Carboniferous 

Although  occupying  a  number  of  small  areas  in  the  northern  portion 
of  the  State  no  clays  of  economic  value  have  been  noted  from  these. 
In  Will's  Valley,  however,  it  carries  an  important  bed  of  white  clay, 
which  is  also  found  farther  north  near  the  State  line.  The  white  clay, 
which  is  known  locally  as  chalk,  and  has  an  aggregate  thickness  of  about 
40  feet,  is  worked  near  the  State  line  about  Eureka  station,  and  thence 
southward  for  two  miles. 

Coal-measures 

These  occupy  a  large  triangular  area  in  the  northern  part  of  the 
State,  but  since  a  great  portion  of  the  region  is  remote  from  the  railways, 
whatever  shales  or  clays  it  may  contain  have  been  but  little  developed. 
The  most  important  deposits  are  the  under-clays  found  in  some  of  the 
coal-fields,  which  have  been  employed  for  making  pottery,  as  at  Jugtown, 
Fort  Payne,  Rodentown,  etc.  The  shales  are  also  used  in  some  parts 
of  the  State  for  making  vitrified  brick,  especially  at  Coaldale  and  North 
Birmingham.  No  fire-clays  have  thus  far  been  found  in  the  coal- 
measures. 


282  CLAYS 


Cretaceous 

This  contains  the  most  important  clay-deposits  in  the  State,  but 
most  of  the  beds  have  thus  far  been  found  in  one  member,  namely, 
the  Tuscaloosa.  This  consists  usually  of  yellow  and  grayish  sands, 
with  smaller  beds  of  pink  and  light-purple  sands  thinly  laminated,  dark- 
gray  clays  holding  many  leaf  impressions,  and  gray  lenses  of  massive 
clay  which  vary  in  color.  The  formation  occupies  a  belt  of  country 
extending  from  the  northwest  corner  of  the  State  around  the  edges  of 
the  Paleozoic  formations  to  the  Georgia  State  line  at  Columbus,  attain- 
ing its  greatest  width  at  the  northwestern  boundary  of  the  State.  The 
purer  clays  have  as  yet  been  found  only  in  the  northern  part  of  this 
area,  in  Fayette,  Marion,  Franklin,  and  Colbert  counties,  and  the  ad- 
joining parts  of  Mississippi,  but  the  following  section  from  12  miles  east 
of  Tuscaloosa  affords  a  good  idea  of  the  character  of  the  deposits. 

SECTION  12  MILES  EAST  OF  TUSCALOOSA,  ALA. 

Feet.     In. 

1.  Purple  massive  clays 5 

2.  Ferruginous  sandstone  crusts 6-8 

3.  Variegated  clayey  sands 10 

4.  Purple  clays  with  sand  partings 10 

5.  Ferruginous  crusts 1 

6.  Laminated,  gray  and  yellow  sandy  clay 6-8 

7.  Lignite  with  pyrite  nodules 2       6 

8.  Dark-gray  massive  clays 6       8 

9.  Covered 1       8 

10.  Purple  clay 

This  section  shows  great  vertical  variation  and  a  similar  one  may 
occur  horizontally.  Nevertheless,  the  formation  contains  not  a  few 
deposits  of  workable  size,  which  are  employed  for  stoneware  and  common 
earthenware,  as  at  Sulligent,  Tuscaloosa,  etc.  In  Colbert  County  the 
Tuscaloosa  formation  carries  fire-clays,  and  other  deposits  are  known 
near  Woodstock  and  Bibbville,  A  curious  white  siliceous  clay  occurs 
near  Chalk  Bluff  and  Pearce's  Mill,  Marion  County,  but  it  has  not  been 
utilized. 


DISTRIBUTION    OF  CLAY  IN   THE   UNITED   STATES  283 


Tertiary 

The  Tertiary  formations  underlie  the  southern  third  of  Alabama,  and 
while  it  is  known  that  they  contain  extensive  deposits  of  clay,  these 
have  been  but  little  investigated.  The  most  promising  occurrences 
of  clay  in  this  section  are  in  the  Grand  Gulf  formation  (Pliocene)  which, 
according  to  Dr.  E.  A.  Smith,  overlies  unconformably  most  of  the  older 
Tertiary  beds.  A  siliceous  clay,  resembling  flint-clay  in  appearance, 
is  found  in  abundance  in  Choctaw,  Clarke,  Conecuh,  and  other  counties. 
Its  analysis  is  given  in  the  appended  table. 


Pleistocene 

Over  much  of  the  coastal  plain  in  the  second  bottoms  of  the  rivers 
there  is  a  great  extent  of  yellow  loam  suitable  for  brickmaking,  which 
corresponds  to  the  Columbia  loams  of  the  Northern  States. 


Division  of  Clays  by  Kinds 

China-clays. — The  only  kaolins  are  those  occurring  chiefly  in  Ran- 
dolph County. 

Fire-clays. — The  fire-clays  of  Alabama  come  from  four  geologic 
horizons,  namely:  (1)  The  Cambrian  and  Silurian  limestone  forma- 
tions of  the  Coosa  Valley  region,  seen  at  Peaceburgh,  Calhoun  County, 
Oaxanna  County,  and  Rock  Run,  Cherokee  County;  (2)  the  cherty 
limestone  of  the  Lower  Carboniferous  formations  of  Will's  Valley,  seen 
at  Will's  Valley  and  Valley  Head,  Dekalb  County;  (3)  the  Tuscaloosa 
formation  of  the  Lower  Cretaceous,  occurrences  being  known  at  Bibb 
ville  and  Woodstock  in  Bibb  County,  Hull  station  and  Tuscaloosa  in 
Tuscaloosa  County,  Potter's  Mills  in  Marion  County,  and  Pegram  in 
Colbert  County;  (4)  the  Lower  Tertiary  formation,  Choctaw  County. 

Pottery-clays. — These  are  found  at  a  number  of  localities,  including 
Blount  County;  Rock  Run,  Cherokee  County;  Fort  Payne,  Dekalb 
County;  Coosada,  Elmore  County;  Bedford  and  Fernbank,  Lamar 
County;  Tuscaloosa,  Shirley's  Mill,  Fayette  County;  Pegram,  Colbert 
County. 

Brick-clays. — Many  deposits  are  found  in  all  parts  of  the  State. 

In  the  following  table  there  are  given  a  number  of  physical  tests 
and  chemical  analyses  of  Alabama  clays.  Additional  ones  will  be  found 
in  Reference  4,  on  page  285. 


284 


CLAYS 


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DISTRIBUTION  OF  CLAY  IN  THE    UNITED  STATES 
LOCALITIES  OF  CLAYS  IN  PRECEDING  TABLE 


285 


No. 

Locality. 

Geological  Age. 

Uses. 

I. 
II. 
III. 
IV. 
V. 
VI. 
VII. 
VIII. 
IX. 
X. 

Gadsden  

Car 

L(H 

Coa 
Lo\ 

i 
f 

abro-Silurian  

1  1             (i 

N 

t 

t 

ot  wor 

t 

( 

ked 

Peaceburg  

Eureka 

ver  Carboniferous  
1-measures.  . 

Birmingham  
Bibbville  

ver  Cretaceous  

1  1 

Bedford  

Shirley's  Mills  

it 

Bexar 

ti 

Pegram 

(  f 

Tuscaloosa 

(  e 

Nos.  I-X  from  Bull.  6,  Ala.  Geol.  Survey. 

References  on  Alabama  Clays 

1.  McCalley,  H.,  Report  on  the  Valley  Regions  of  Alabama  (PalsR- 
ozoic  strata):    Clays.     In  two  parts.     I.  The  Tennessee  Valley  Region, 
Ala.  Geol.  Surv.,  p.  68,  1896. 

2.  Ibid.,  II.  The  Coosa  Valley  Region,  p.  84,  1897. 

3.  Mell,  P.  H.,  Jr.,  The  Southern  soapstones,  kaolin,  and  fire-clays 
and  their  uses,  Amer.  Inst.  Min.  Eng.,  Trans.,  X,  p.  318,  1882. 

4.  Ries,  H.,  The  Clays  of  Alabama,  Ala.  Geol.  Surv.,  Bull.  6,  p.  220, 
1900. 

5.  Smith,  E.  A.,  The  Clay  Resources  of  Alabama  and  the  industries 
dependent  on  them,  Eng.  and  Min.  Jour.,  LXVI,  p.  369,  1898. 

6.  Smith,  E.  A.,  Geological  relations  of  the  clays  of  Alabama,  Ala. 
Geol.  Surv.,  Bull.  6,  pp.  69-113,  1900. 

Arkansas 

In  the  Mesozoic  regions  of  Arkansas  there  are  found  a  great  variety 
cf  clays.  Those  occurring  within  the  Tertiary  region  are  said  to  have 
been  used  for  the  manufacture  of  pottery,  while  kaolin  is  said  to  occur 
in  Pike,  Pulaski,  Saline,  and  Ouachita  counties,  but  the  beds  are  rarely 
over  2  feet  in  thickness.  The  Pulaski  deposits  are  the  only  true  kaolins 
of  those  mentioned. 

Brick-clays  are  abundant  in  the  Pleistocene  formations.  The  shales 
associated  with  the  Carboniferous  coals  should  also  prove  of  value  for 
the  manufacture  of  clay-products.  According  to  Branner  they  occur 
in  great  abundance  between  Little  Rock  and  Fort  Smith.1 

The  following  analyses  are  given  by  Branner  in  the  paper  referred  to 
above : 

1  Branner,  Amer.  Inst.  Min.  Eng.,  Trans.,  XXVIII,  p.  42,  1897. 


286 


CLAYS 


ANALYSES  OF  ARKANSAS  CLAYS 


I 

II. 

111. 

IV. 

V. 

VI. 

VII. 

VIII. 

IX. 

Silica  (SiO2)..  . 

53.30 

62.36 

58.43 

51.3 

63.07 

48.34 

76.33 

75  .  99 

45.28 

Alumina 

23.29 

25.52 

22.50 

24.69 

23.92 

34.58 

16.04 

16.12 

37.39 

(A1203), 

Ferric       oxide 

9.52 

2.16 

8.36 

10.57 

1.94 

1.65 

1.24 

1.35 

1.71 

(FeAO  

Lime  (CaO).  .  . 

.36 

.51 

.32 

.32 

.23 

.81 

1  By 

f 

1.83 

Magnesia 

diff. 

(MgO) 

1.49 

.29 

1.14 

.63 

trace 

trace 

.99 

1.45<j 

.29 

Potash  (K2O)  . 

1.36 

1.90 

2.18 

2.18 

1.15 

.44 

] 

Soda  (Na2O).  . 

2.76 

.66 

1.03 

.72 

1.08 

1.26 

J 

I 

Water  (H2O)  . 

5.16 

5.32 

6.87 

9.11 

7.07 

12.94 

5.40 

13.49 

Total  

97.24 

98.72 

100.83 

99.31 

99.46 

100.  02  ' 

100.00 

94.91 

99.99 

I.  Clay-shale  from  railroad  cut  at  south  end  of  upper  bridge,  Little  Rock. 
II.  Decayed  shale  from  Iron  Mountain  Railroad  cut,  at  crossing  of  Mt.  Ida  road,  Little  Rock. 

III.  Clay-shale  from  Nigger  Hill,  Little  Rock. 

IV.  From  S.  E.  i  of  S.  W    i.  Sec.  31,  10  N.,  23  W. 
V.   Benton,  Hick's  bed,  2  S..  15  W.,  Sec.  12. 

VI.  Benton,  Howe's  pottery 

VII.  John  Foley'*,  13  S.,  24  W  ,  Sec.  18,  N.  E.  i  of  S.  E.  i. 
VIII.  Climax  pottery,  15  S..  28  W.,  Sec.  5,  W   *  of  S.  E.  i. 
IX.  Kaolin,  1  N.,  12  W.,  Sec.  36,  Tarpley's. 

I-IV,  Carboniferous;  V-IX,  Tertiary.     Branner,  Ref.  1. 

References  on  Arkansas  Clays 

1.  Branner,  J.  C.,  Cement  Materials  of  Southwestern   Arkansas,  in 
Amer.  Inst.  Min.  Eng.,  Trans.,  XXVII,  p.  42,  1897. 

2.  Annual  Report  of  State  Geologist  for  1888,  Pt.  V,  p.  11.     Gives 
numerous  analyses. 

Arizona 

The  clay  resources  of  this  State  have  been  but  little  developed. 

Ransome 2  states  that  clay  for  use  in  a  mixture  to  line-converters 
is  obtained  from  near  the  Czar  fault  in  the  Copper  Queen  mine,  and 
has  been  formed  by  decomposition  or  alteration  of  the  Obrigo  lime- 
stone. 

Common  brick-clays  are  used  locally  at  a  few  points. 

California 

Published  information  regarding  the  properties  of  the  California 
clays  is  very  meager,  although  many  scattered  references  are  to  be 
found  in  the  annual  reports  of  the  California  State  Mineralogist,  espe- 
cially the  7th  to  13th. 

Residual  clays  are  derived  from  many  of  the  formations  occurring 
within  the  State,  and  are  occasionallv  worked  for  common  brick. 


TiO2,  156. 


U.  S.  Geol.  Altas,  Folio  No.  112,  p.  17. 


PLATE  XXIII 


FIG.  1. — Pit  of  Carboniferous  shale  near  Birmingham,  Ala.     (Graves  photo. ) 


FIG.  2. — Tertiary  clays  (lone  formation)  used  for  brick,  terra-cotta,  etc., 
Lincoln,  Calif.     (Photo  loaned  by  Gladding,  McBean  &  Co.) 


DISTRIBUTION   OF  CLAY  IN  THE  UNITED  STATES  289 

Of  the  sedimentary  clays,  those  belonging  to  the  lone  formation 
of  the  Neocene,  extensively  developed  in  the  Great  Valley,  are  the  most 
important,  but  unfortunately  they  are  exposed  in  only  a  few  places. 

Lindgren  l  states  that  the  white  clays  of  this  formation  are  frequently 
well  suited  to  pottery  manufacture,  and  the  clay  industry  has  been 
extensively  developed  around  Lincoln,  Placer  County.  Similar  beds 
are  found  at  many  places  in  the  Cosumnes  area,  but  they  are  not  worked. 

The  white  lone  clays  have  also  been  extensively  dug  to  the  north- 
west of  lone  and  above  Carbondale,  to  be  used  in  making  coarse  pottery. 
A  variegated  clay  of  good  quality  has  been  quarried  at  Valley  Springs 
and  shipped  to  Stockton  for  making  pottery.2 

A  belt  of  clays  is  also  said  to  extend  in  a  general  west  of  north  and 
east  of  south  direction  from  Elsinore  on  the  south  to  Corona  on  the 
north.  These  have  been  dug  for  the  factories  at  Elsinore,  Corona,  and 
Los  Angeles.3 

At  Los  Angeles  the  Tertiary  clays  are  used  locally  for  brick  and 
flower-pots. 

The  Lincoln  locality,  although  the  smallest  of  the  three  important 
ones,  is  extensively  worked;  the  Carbondale  area  contains  probably 
the  best  grades  of  clay,  but  the  Elsinore-Corona  belt  affords  a  greater 
variety. 

References  on  California  Clays 

1.  Anon.,   Industrial    Materials   of   California,   Calif.    State   Mining 
Bureau,  Bull.  38,  1906. 

2.  Johnson,  W.  D.,  Clays,  Calif.  State  Mineralogist,  9th  Ann.  Kept., 
287,  1890. 

3.  Ries,  H.,  The  Clay-working  Industry  of  the  Pacific  Coast  States, 
Mines  and  Minerals,  XX,  p.  487,  1900. 

4.  See  scattered  notes  in  Annual  Reports  of  California,  State  Miner- 
alogist, up  to  the  13th. 

Colorado 

The  clay-bearing  formations  of  Colorado  which  have  been  thus  far 
examined  or  developed  are  chiefly  Cretaceous,  Tertiary,  and  Quarter- 
nary. 

1  U.  S.  G.  S.,  Geol.  Atlas,  Folio  5. 

2  Turner,  U.  S.  Geol.  Survey,  Geol.  Atlas,  Folio  11. 

3  Bull.  38,  Calif.  State  Min.  Bureau,  1906. 


290  CLAYS 

Mesozoic 

The  Cretaceous  and  Tertiary  beds  are  well  exposed  along  the  eastern 
edge  of  the  Rocky  Mountains,  where  they  have  been  worked  for  some 
years. 

In  the  Denver  Basin,  which  is  the  most  important,1  the  clays  are 
derived  from  the  Denver,  Laramie,  Fox  Hills,  and  Dakota  formations, 
but  the  second  and  fourth  are  comparatively  unimportant. 

The  Dakota  formation  in  the  Denver  Basin  carries  beds  of  fire-clay 
which  occur  as  non-continuous  bands  5  to  15  feet  thick  and  several 
hundred  feet  in  length,  in  the  argillaceous  shales  which  separate  the  two 
or  three  heavy  layers  of  sandstones  that  constitute  the  bulk  of  the 
formation,  and  forms  the  hogbacks  around  Golden  (PL  XXIV,  Fig.  2). 
The  fire-clays,  some  of  which  fuse  at  cone  33,  are  bluish-gray  or  black 
in  color,  the  impurities  consisting  of  sand  laminae,  and  iron  oxide  result- 
ing from  the  decomposition  of  pyrite. 

The  Golden  clay  enjoys  a  high  reputation  for  fire-brick  and  assayer's 
materials.  Fire-clays  also  exist  in  the  Laramie  in  connection  with  the 
coal,  but  these  are  of  inferior  quality  and  irregular  thickness. 

The  Dakota  clays  have  also  been  worked  at  Parkdale,  west  of  Pueblo, 
to  supply  the  fire-brick  works  at  the  latter  locality. 

The  upper  half  of  the  Fox  Hills  formation  carries  an  abundance  of 
slightly  arenaceous  clays  suitable  for  structural  materials,  and  these 
have  been  worked  at  both  Golden  and  Valmont. 

At  Boulder,  Boulder  County,  the  Pierre  shales  of  the  Cretaceous 
afford  an  excellent  supply  of  material  for  common,  pressed,  and  paving 
brick,  but  the  material  seems  to  vary  in  its  physical  properties  from 
place  to  place  (Ref.  2).  The  Carlisle  shale  has  been  worked  at  La  Junta 
for  red  dry-pressed  brick. 

Pleistocene 

,  The  loess  is  used  at  many  points  in  eastern  Colorado  for  making 
common  brick,  and  many  brick-yards  around  Denver  are  supplied  with 
it.  At  other  localities  alluvial  clays  are  easily  obtained. 

References  on  Colorado  Clays 

1.  Eldridge,  Cross  and  Emmons,  Geology  of   Denver  Basin,  U.  S. 
Geol.  Surv.,  Mon.  XXVII,  p.  387,  1896. 

2.  Fenneman,    N.  M.,  Geology   of   Boulder    District,    Colo.,    U.    S. 
Geol.  Surv.,  Bull.  265,  p.  72,  1905. 

1  See  references  1,  3,  4,  and  5  on  Colorado. 


PLATE  XXIV 


FIG.  1. — Tertiary  clays  used  for  common  brick,  Los  Angeles,  Calif.     (From 
Bull.  38,  Calif.  State  Min.  Bur.) 


FIG.  2. — View  of  fire-clay  pits,  Golden,  Colo.     The  good  clay  has  been  taken  out. 
the  worthless  sandy  beds  left  standing.      (Photo  by  H.  Ries.) 

291 


DISTRIBUTION  OF  CLAY  IN   THE   UNITED  STATES 


293 


3.  Geijsbeek,  S.,  Colorado  Clays,  Clay-worker,  XXXVI,  p.  424. 

4.  Ries,  H. ,  The  Clays  and  Clay  Industry  of  Colorado,  Amer.  Inst. 
Min.  Eng.,  Trans.,  XXVII,  p.  336,  1898. 

5.  Ries,  H.,  U.  S.  Geol.  Surv.,  18th  Ann.  Rept.,Pt.  V  (ctd.),  p.  1131, 
1897. 

ANALYSES  OF  COLORADO  CLAYS 


I. 

II. 

III. 

IV. 

Silica  (SiO2)                              

50  35 

63  309 

46  61 

63  22 

Alumina  (AlgOa)                           

33  64 

14  38 

37  20 

24  72 

Ferric  oxide  (Fe2Oa).  ...         

.75 

6  27 

15 

43 

Ferrous  oxide  (FeO)  

.859 

Lime  (CaO)  

1  81 

44 

30 

Magnesia  (MgO).  .       

trace 

2  57 

25 

13 

Potash  (K2O)  

.49 

1  28  1 

Soda  (Na2O)  

.09 

2  19  / 

1.23 

trace 

Titanic  acid  (TiO2)  

.80 

68 

Water  (H2O)  

11.75 

5  223 

13  65 

8  63 

Moisture 

2  13 

2  05 

47 

1  36 

40 

Total 

100  00 

99  941 

100  00 

99  87 

I.  A  typical  Golden  fire-clay.  U.  S.  G.  S.,  Mon.  XXVII,  p.  390. 

II.  Pierre  shale,  Lee  yard,  Boulder,  Boulder  County,  U.  S.  G.  S.,  Bull.  265,  p.  74. 

III.  Edgemont,  Jefferson  County, )  ,T    a    „    _     ,_.,     .          D      ,      D,    .„  __.   ___ 

IV.  Pueblo,  Pueblo  County,  I  U.  S.  G.  S.,  16th  Ann.  Kept.,  Pt.  IV,  pp.  554-565. 


Connecticut 

The  clays  at  present  worked  in  this  State  are  confined  to  the  central 
lowland  portion  of  the  State,  and  to  West  Cornwall  in  Litchfield 
County. 

Residual  Clays 

At  West  Cornwall,  Litchfield  County  (PL  XXV,  Fig.  1),  there  is  a 
deposit  of  koalin,  which  has  been  formed  by  the  weathering  of  a  bed 
of  feldspathic  quartzite,  but  has  been  protected  from  glacial  erosion, 
partly  because  of  its  location  in  a  hollow,  and  partly  because  of  its  being 
interbedded  with  harder  quartzites.  It  is  of  white  color,  and  sandy 
or  granular  texture.  The  deposit  which  has  a  length  of  at  least  1000 
feet  dips  southeastward  at  a  rather  steep  angle  and  is  worked  by  forcing 
water  down  through  pipes  and  washing  out  the  clay,  which  is  then  brought 
up  in  suspension  and  floated  down  to  the  settling-tanks.  This  clay  is 
sold  to  potters  and  paper  manufacturers.  An  analysis  of  the  washed 
material  is  given  below. 


294 


CLAYS 


o 


•tf  -I 


DISTRIBUTION  OF  CLAY  IN    THE  UNITED  STATES  295 


Pleistocene 

Nearly  all  of  the  workable  clay-deposits  of  Connecticut  are  of  this 
age,  and  were  deposited  either  in  estuaries  at  a  time  when  the  land 
stood  at  a  lower  level,  thus  allowing  the  water  to  occupy  some  of  the. 
valleys  entering  Long  Island  Sound,  or  else  they  were  laid  down  in 
lakes,  formed  by  the  damming  of  the  valleys  by  glacial  drift.  The 
valley  of  the  Quinnipiac  depressed  below  sea-level,  became  a  long,  deep 
estuary  in  which  the  fine  clay  derived  from  the  material  in  and  under  the 
ice  was  deposited. 

The  Milldale,  Berlin,  Middletown,  and  Cromwell  clays  are  lake- 
deposits. 

The  central  Connecticut  clays  are  grouped  by  Loughlin  into  five- 
areas,  as  follows: 

Northern  area,  the  largest  in  the  State  and  including  the  brick-yards 
in  and  north  of  Hartford.  The  clay  is  a  blue  or  sometimes  red 
deposit  of  highly  plastic  character,  alternating  with  layers  of  fine 
quicksand. 

This  area  extends  from  King's  Island  to  eastern  Rock  Hill  County. 
At  Hartford  it  lies  chiefly  west  of  the  river  and  is  4  to  5  miles  in  width, 
thence  it  extends  northeastward  to  South  Windsor,  where  east  of  the 
river  its  width  is  2  to  5  miles.  Its  thickness  varies  from  a  few  feet 
to  as  much  as  95.  At  most  points  the  clay  is  overlain  by  a  varying 
thickness  of  red  or  yellow  sand. 

Clayton  area,  a  small  area  of  reddish  clay,  having  a  depth  of  not 
less  than  15  or  20  feet  and  overlain  by  coarse  sand. 

Berlin  area,  a  brownish-red  clay-deposit  in  the  valley  of  the  Sebeth 
River  between  Berlin  and  Middletown. 

Quinnipiac  area,  including  the  clays  extending  from  North  Haven 
southward  into  New  Haven.  The  clay  is  similar  to  that  of  the  Berlin 
region,  and  is  usually  overlain  by  several  feet  of  peat.  Its  measured 
thickness  ranges  from  6  to  30  feet. 

Milldale  area.  This  is  the  smallest  of  the  worked  deposits.  In 
character  the  material  is  similar  to  the  others. 

All  of  these  Pleistocene  clays  are  used  chiefly  for  the  manufacture 
of  common  brick,  although  a  small  quantity  of  the  drain-tile  and  earthen- 
ware is  also  produced.  The  stoneware  and  fire-brick  manufactured 
in  Connecticut  are  from  New  Jersey  clays. 

The  following,  analyses  are  taken  from  Loughlin's  report  referred  to 
below. 


296 


CLAYS 


ANALYSES  OF  CONNECTICUT  CLAYS 


I. 

II. 

III. 

IV. 

V. 

VI. 

Silica  (SiO2)  

47.50 

52.73 

50.33 

55.27 

58.02 

56  75 

.Alumina  (AlgOa)  

37.40 

22  .  25 

27.06 

20.52 

17.93 

17  54 

Ferric  oxide  (Fe2Oi)  . 

0  80 

3  14 

2  29 

5  34 

4  89 

4  92 

ferrous  oxide  (FeO) 

4  55 

2  62 

1  55 

1  24 

0  93 

Lime  (CaO) 

trace 

1  48 

1  22 

2  21 

3  42 

4  18 

.Magnesia  (MfirO). 

3  20 

3  34 

2  80 

1  92 

2  34 

Soda  (Na2O) 

\  1 

/  2  22 

1  78 

2  82 

3  33 

3  40 

Potash  (K2O)  

>  1.10 

\4.28 

4.40 

3.43 

3.06 

3.16 

Water  (H2O)          

12  48 

1.12 

1.42 

1  37 

0  99 

1.24 

JVloisture     •             

4.91 

5.24 

5.06 

5  36 

6  28 

day  substance           

99.00 

Ouartz                      

1.00 

"Clay  base                         

34.15 

47.36 

34.04 

28.75 

27.82 

Non-fluxing  impurities  

46.86 

36.69 

48.18 

53.55 

53.99 

Tluxes.  .                               

18.87 

15.65 

18.15 

17.86 

18.93 

I.   We*t  Cornwall,  kaolin,  H    Ries.  anal. 
II.   S.  Windsor,  Conn.,  East  Windsor  Hill  Brick  Co. 
III.    NewfieM,  Tuttle  Bros. 
IV    Berlin,  Berlin  Brick  Co. 
V    North  Haven.  I.  L.  Stiles  &  Sons. 

References  on  Connecticut  Clays 

1.  Loughlin,  G.  F.,  The  Clays  and  Clay  Industries  of  Connecticut, 
Conn.  Geol.  and  Nat.  Hist.  Surv.,  Bull.  4,  1905. 

2.  Sheldon,  J.  M.  A.,  Concretions  from  the  Champlain  Clays  of  the 
Connecticut  Valley,  45  pp.,  1900,  Boston,  Mass.;    Abstracted  in  Amer. 
Jour.  Sci.,  4th  ser.,  Vol.  11,  p.  397,  1901. 

Delaware 

The  clay  resources  of  this  State  are  of  comparatively  little  import- 
ance, nor  has  much  been  published  regarding  them.  In  the  north- 
western part,  along  the  Pennsylvania  boundary,  there  are  deposits  of 
kaolin  similar  to  those  found  in  southeastern  Pennsylvania.  The  prod- 
uct is  washed  before  shipment. 

The  Potomac  beds  of  the  coastal  plain  area  are  said  to  contain  stone- 
ware and  fire-clays,  which  have  been  dug  at  two  localities  not  far  from 
Wilmington. 

District  of  Columbia 

According  to  Darton  1  there  is  an  abundance  of  brick-clay  around 
Washington  and  much  of  it  is  used,  in  fact  large  areas  have  been  dug 
over  in  the  immediate  vicinity  of  the  city.  The  materials  employed 


1  U.  S.  Geol.  Atlas,  Folio  No.  70,  Washington,  D.  C. 


DISTRIBUTION  OF  CLAY   IN  THE  UNITED  STATES  297 

are  chiefly  loams  belonging  to  the  Columbian  formation,  but  the  sandy 
clays  of  the  Potomac  beds  are  also  used. 

Florida 

The  clays  of  Florida  are  mostly  surface  deposits  of  Tertiary  and 
Pleistocene  age,  and  occur  chiefly  in  the  northern  part  of  the  State,  the 
majority  of  them  being  more  or  less  sandy  in  their  character,  and  adapted 
to  little  else  than  common  brick.  They  have  been  worked  to  some  ex- 
tent around  Jacksonville,  and  also  at  a  few  other  localities.  While  most 
of  these  are  ferruginous,  calcareous  ones  are  also  known,  and  have  been, 
noted  from  several  localities  as  18  miles  southwest  of  Tallahassee,  and 
one  half  mile  southeast  of  Jackson  Blutf.  Their  composition  is  given 
below. 

The  ball-clays  are  the  most  important  ones  found  in  the  State.  These 
are  white-burning,  plastic,  sedimentary  clays,  of  high  refractoriness, 
which  are  much  used  by  the  white-ware  potteries.  The  clay  occurs  at 
several  points  in  northcentral  Florida  (Fig.  36),  and  the  different  areas 
may  represent  portions  of  a  formerly  continuous  bed.  It  consists  of  a 
mixture  of  white  clay  and  quartz  pebbles,  the  latter  forming  65  to  75 
per  cent  of  the  entire  mass.  A  section  measured  in  the  pit  at  Edgar  l 
gave: 

Top-soil 8     ft. 

Impure  upper  clay 8-10  " 

White  clay 25     " 

Green  clay 

The  thickness  of  the  green  clay  is  not  exactly  known,  but  at  some 
localities  it  appears  to  rest  on  limestone.  An  extensive  belt  of  ball- 
clay  also  occurs  along  the  Palatlakaha  River  south  of  Leesburg,  and  at 
Bartow  Junction. 

On  page  298  are  given  analyses  of  both  the  calcareous  clays  and 
the  ball-clays. 

References  on  Florida  Clays 

1.  Memminger,  C.  G.,  Florida  kaolin-deposits,  Eng.  and  Min.  Jour., 
LVII,p.  436,  1894. 

2.  Ries,  H.,  The  Clays  of  Florida,  U.  S.  Geol.  Surv.,  17th  Ann.  Kept., 
Pt.  Ill,  p.  871,  1898. 

3.  Ries,  H.,  See  Florida,  U.S.  Geol.  Surv.,  Prof.  Pap.  11,  p.  81,  1903 

1  See  Reference  2  below. 


298 


CLAYS 

ANALYSES  OF  FLORIDA  CLAYS 


I. 

11. 

III. 

IV. 

Silica  (SiO2)  

35  95 

30  83 

46  11 

45  39 

Alumina  (A^Oa)  

13  23 

15  40 

39  5 

39  19 

Ferric  oxide  (F^Os) 

1  27 

1  40 

35 

4^ 

Lime  (CaO)  

15  00 

13.78 

51 

Magnesia  (MgO)  

5.40 

7  50 

13 

29 

AJkalies  (Na2O,K2O)  

undet. 

83 

Water  (H2O)             

10.55 

7.16 

13  78 

14  01 

Carbon  dioxide  (COa) 

18  50 

20  14 

Sulphur  trioxide  (SOs) 

07 

Total       

99.90 

96.21 

99.94 

100  67 

I.   Calcareous  clay,  Leon  County,  H.  Hies.  anal. 
II.  Calcareous  clay,  near  Jackson  Bluff  on  Ocklocknee  River,  H.  Ries,  anal. 

III.  Washed  clay  from  Palatlakaha  River. 

IV.  Washed  clay  from  Edgar,  C.  Langenbeck,  anal. 
I-IV  from  U.  S.  Geol.  Surv.,  Prof.  Pap.  11,  p.  83. 

Georgia 

This  State  is  divisible  geologically  into  three  areas,  namely:  (1)  A 
northwestern  area,  underlain  by  shales,  limestones,  and  sandstones  of 
Palaeozoic  age;  (2)  a  broad  central  belt  of  pre-Cambrian  rocks,  such 
as  granites  and  gneisses;  (3)  a  southeastern  belt,  in  the  coastal  plain 
region  composed  of  unconsolidated  sedimentary  rocks  of  Cretaceous, 
Tertiary,  and  Pleistocene  age. 

Palaeozoic  Area 

This  belt  includes  the  counties  of  Polk,  Floyd,  Bartow,  Gordon,  Mur- 
Tay,  Whitfield,  Catoosa,  Chattooga,  Walker,  and  Dade,  and  while  the 
rocks  in  this  area  range  from  Cambrian  to  Carboniferous  inclusive,  the 
residual  clays  derived  from  them  are  all  somewhat  similar.  The  shales 
are  often  calcareous,  with  the  exception  of  the  Carboniferous  ones.  The 
residual  clay-deposits,  which  are  chiefly  adapted  to  common-brick  man- 
ufacture, are  often  of  considerable  extent,  and  generally  ferruginous 
character,  but  here  and  there  contain  pockets  of  white  clay  which  may 
be  suitable  for  fire-brick;  those  derived  from  the  limestones  often  con- 
tain cherty  nodules. 

Pre-Cambrian  Belt 

This  covers  an  area  of  about  12,000  square  miles,  and  consists  of 
-granites,  gneisses,  schists,  marbles,  and  in  places  pegmatite  veins,  of 
which  the  last  should  afford  kaolin.  Residual  clays  are  abundant 
throughout  the  region,  and  the  wash  from  them  may  form  secondary 
-.deposits  in  the  valleys. 


PLATE  XXV 


FIG.  1.— Kaolin-pit  at  West  Corn  wall,  Conn.    (Photo  loaned  by  The  Kaolin  Company.) 


FIG.  2. — White  clay  and  sands  of  Cretaceous  age,  overlain  by  Tertiary  beds,  Rich 
Hill  near  Knoxville,  Ga.  (After  G.  E.  Ladd,  Ga.  Geol.  Surv.,  Bull.  6A,  p.  32, 
1898.) 

299 


DISTRIBUTION   OF  CLAY  IN  THE  UNITED  STATES  301 


Coastal  Plain  Region 

This  region  includes  that  portion  of  the  State  lying  to  the  southeast 
of  a  line  drawn  through  Augusta,  Macon,  and  Columbus,  and  coinciding 
approximately  with  the  fall  line  (Fig.  50). 

Within  this  area  the  formations  range  from  Cretaceous  to  Pleistocene 
and  carry  many  clay-deposits  of  variable  character,  ranging  from  easily 
fusible  ferruginous  clays  to  snowy  white  ones  (PL  XXV,  Fig.  2)  of 
high  refractoriness.  The  form  of  most  of  these  is  rather  irregular  (a 
characteristic  of  most  coastal  plain  clays),  the  majority  being  lens 
.shaped,  and  surrounded  by  sand  or  sandy  clay. 

Of  the  several  formations,  the  Cretaceous  has  the  smallest  surface 
area,  forming  a  triangle,  the  base  of  which  is  on  the  Chattahoochee 
River,  the  apex  at  Macon,  and  the  northwest  side  agreeing  with  the 
fall  line.  Nevertheless,  this  area  includes,  so  far  as  known,  the  most 
important  clays  found  in  Georgia.  The  Cretaceous  shows  a  section  of 
.about  1640  feet  of  southeasterly  dipping  beds,  which  are  well  exposed 
along  the  Chattahoochee  River  below  Columbus,  and  other  good  expo- 
sures occur  along  the  Georgia  Central  Railroad,  between  Columbus  and 
Macon,  but  the  best  clays  are  found  in  the  region  around  Griswoldville, 
about  10  miles  east  of  Macon.  In  this  last  area,  which  includes  the 
southern  half  of  Jones  and  Baldwin  counties  and  the  northern  half  of 
Twiggs  and  Wilkinson,  the  clays  are  6  to  10  feet  thick,  often  white  in 
.color,  free  from  grit,  and  with  a  soapy  feel,  due  to  the  presence  of  many 
muscovite  scales  of  microscopic  size.  Other  exposures  occur  in  the 
vicinity  of  Lewiston,  Gordon,  Mclntyre,  Augusta,  Butler,  etc.  The 
following  section  given  by  Ladd  from  Lewiston  is  fairly  typical  of  their 
occurrence : 

Feet. 

1.  Red  and  yellow  clayey  sand,  with  seams  of  laminated  clay;   also  thin 

seams  of  limonite  with  coarse  pebbles 6 

2.  Irregular   siliceous   beds   resembling  quartzite,   and   containing  drusy 

quartz  cavities  and  many  fragments  of  shells 4 

3.  White  sand,  free  from  iron  stain,  at  times  cross-bedded,  and  contain- 

ing mica  and  white  clay 7 

4.  White  clay,  free  from  grit 7 

5.  White  sand  at  bottom 2 

The  following  analyses  and  tests,  taken  from  the  reports  of  Ladd 
and  Spencer,1  represent  the  character  of  some  of  the  Georgia  materials. 

1  See  references  at  end  of  Georgia. 


302 


CLAYS 


DISTRIBUTION   OF  CLAY  IN  THE   UNITED  STATES  303 

ANALYSES  AND  PHYSICAL  TESTS  OF  GEORGIA  CLAYS 


I. 

II. 

ill. 

IV. 

V. 

VI. 

Silica  (SiOo) 

41  20 

52  82 

46  17 

56  28 

46  62 

77  AH 

Alumina  (A^Os). 

38  60 

26  17 

39  13 

14  64 

38  28 

10  QO 

Ferric  oxide  (Fe2O3)  
Lime  (CaO).  . 

1.45 

9.46 
trace 

0.45 
0  18 

0.28 

7  08 

1.02 
0  18 

2.25 

Magnesia  (MgO).  ... 

0  30 

1  08 

0  11 

1  71 

0  fi^ 

Potash  (ICO)  

0  09 

2  71 

0  51 

1  » 

0  05 

1    83 

Soda  (Na2O)  

0  02 

0  20 

0  63 

j  4.  23 

0  08 

0  32 

Water  (H2O)  

16  35 

7  00 

Ism 

If?n 

Isrn 

Moisture 

0  35 

0  23 

13.08 
0  57 

11.24 

8  7 

13.64 

0  72 

4.70 
0  2ft 

Titanic  oxide  (TiO2)  

1.95 

with 

1  98 

Tensile  strength  

A1203 

25 

213 

24 

Air-shrinkage   .                   .    . 

8 

25 

8 

Fire-shrinkage  

6 

2 

Cone  of  fusion  

36 

35 

Specific  gravity  

1  76 

9-1   2 

1  69  to 

Color  when  burned  

buff 

1.75 

yellow 

No. 

Locality. 

Geological  Ages. 

Uses. 

I. 

Flowery  Branch  

Silurian.  .     .  . 

Not  worked 

II 

Near  Cartersville.  . 

Oostanaula  series 

III. 

Griswoldville  

Potomac  clay   . 

IV 

Fitzpatrick. 

Tertiary 

Not  worked 

v 

Steven's  pottery.  . 

Potomac 

Fire-brick     pottery 

VI. 

Rome  

Columbia  .  . 

and  sewer-pipe. 

References  on  Georgia  Clays 

1.  Ladd,  G.  E.,  Preliminary  Report  on  Clays  of  Georgia,  Ga.  Geol. 
Surv.,  Bull.  6A,  204  pp.,  1898. 

2.  Ladd,  G.  E. ,  Notes  on  the  Cretaceous  and  Associated  Clays  of 
Middle  Georgia,  Amer.  Geol.,  XXIII,  p.  240,  1899. 

3.  Spencer,  J.  W.,  The   Palaeozoic   Group,  Ga.   Geol.  Surv.,   1893, 
p.  276. 

4.  See  also  U.  S.  Geol.  Surv.,  Geol.  Atlas  Folios  relating  to  Georgia. 

Illinois 


The  clay  materials  of  this  State  are  obtainable  from  the  Ordovician, 
the  coal-measures,  and  the  drift. 


304  CLAYS 


Ordovician 

So  far  as  known  this  is  of  little  importance,  but  the  Cincinnati  shales, 
outcropping  in  Daviess  and  Boone  counties,  may  prove  of  value  for 
the  manufacture  of  brick,  hollow  brick,  and  perhaps  earthenware,  since 
the  same  material  has  been  successfully  used  in  Iowa,  and  tested  with 
good  results  in  Wisconsin. 

Coal-measures 

These  underlie  a  large  area  in  central,  eastern,  and  southern  Illinois, 
within  a  line  passing  from  Hampton  in  Rock  Island  County,  to  the 
junction  of  the  Kankakee  and  Iroquois  rivers,  thence  southward  to 
near  Chatsworth  in  Livingston  County  and  eastward  to  tne  Indiana 
boundary. 

The  coal-measures  consist  of  a  series  of  coal-beds,  shales,  sandstones, 
and  clays,  those  underlying  the  coal  being  sometimes  of  a  refractory 
character.  Owing  to  the  nearly  horizontal  position  of  the  beds,  mining 
is  usually  carried  on  by  shaft,  although  at  several  localities ,  as  Galesburg, 
etc.,  great  outcrops  of  shale  occur. 

Unfortunately,  the  published  information  regarding  these  Carbonifer- 
ous clays  and  shales  is  not  of  recent  character,  although  they  form  the 
basis  of  an  active  clay- working  industry,  and  are  much  used  for  paving- 
brick  around  Galesburg,  111.  A  number  of  localities  are  mentioned  by 
Worthen  in  the  old  report  of  the  Geological  Survey  of  Illinois  (see  below) 

Tertiary  Clays 

In  Pulaski  and  Alexander  counties  the  Tertiary  contains  beds  of 
pottery-clay,  as  at  Mound  City  on  the  Ohio  River  and  near  Santa  Fe. 


Drift-clays 

These  form  a  most  abundant  source  of  brick-  and  tile-clays  in  many 
parts  of  the  State.  Around  Chicago  these  clays  are  lake-deposits  of 
considerable  extent,  but  they  are  highly  calcareous  and  often  pebbly. 
They  form  the  basis  of  a  large  local  brick  industry,  and  the  smoother 
ones  have  been  used  for  drain-tile  and  even  roofing-tiles.  In  other 
parts  of  the  State  the  clays  are  found  either  in  the  glacial  drift  or  under- 
lying terraces  along  the  broader  rivers,  especially  the  Illinois. 

The  sandy  loess-clay  is  much  used  at  many  points. 


PLATE  XXVT. 


FIG.  1. — Carboniferous  shale  used  for  paving-brick.     Galesburg.  111.     The  excavat- 
ing is  done  with  a  steam-shovel.     (Photo  loaned  by  111.  Geol.  Surv.) 


pIG   2. — View  in  Knobstone  shale-pit,  Crawfordsville,  Ind.      (After  Blatchley, 
Ind.  Dept.  Geol.  and  Nat,  Res.,  29th  Ann.  Kept.,  1895.) 

305 


DISTRIBUTION   OF  CLAY   IN   THE   UNITED  STATES  307 

References  on  Illinois  Clays 

1.  Leverett,  F.,  The  Illinois  Glacial  Lobe,  U.  S.  Geol.  Surv.,  Mon. 
XXXVII.     Describes  distribution  of  drift,  but  is  not  a  paper  of  eco- 
nomic character. 

2.  Worthen,  A.  H.,  Reports  on  Economic  Geology  of  Illinois,  111. 
Geol.  Surv.,  I,  II,  III. 

Indiana 

The  Ordovician,  Silurian,  Devonian,  and  Carboniferous  contain  ex- 
tensive shale-deposits,  but  only  the  last  have  thus  far  proven  of  com- 
mercial value. 

Ordovician 

The  Ordovician  rocks  outcrop  only  in  the  southeast  corner  of  the 
S  ate,  and  there  are  often  covered  by  a  thin  drift  layer.  The  only  shales 
are  the  Hudson  River,  but  these  are  too  calcareous  to  use,  and  of  no 
value  even  when  weathered. 

Silurian 

The  beds  of  this  age  underlie  a  large  area  in  eastern  and  northcen- 
tral  Indiana,  but  carry  few  shales,  and  these  are  of  no  value. 

Devonian 

The  Devonian  beds  underlie  a  great  area,  extending  northwest  and 
southeast  through  central  part  of  State,  but  offer  little  promise  to  the 
clay-worker,  as  they  are  usually  too  bituminous. 

Mississippian  or  Lower  Carboniferous 

The  rocks  of  this  age  afford  residual  clays  and  shales. 

Residual  clays. — Since  a  large  part  of  the  Mississippian  area  occurs 
in  the  driftless  region,  the  residual  clays  derived  from  underlying  lime- 
stone and  sandstones  are  available,  and  occur  at  many  points  in  Monroe, 
Lawrence,  Orange,  Harrison,  and  Floyd  counties,  as  well  as  parts  of  the 
adjoining  ones,  so  that  they  form  the  most  important  source  of  the 
brick-  and  tile-clays  worked  in  these  counties. 

Shales. — Those  of  the  Knobstone  formation  (Fig.  51)  are  important 
and  destined  to  become  prominent  in  the  future,  although  they  have 
been  neglected  in  the  past.  Indeed  they  are  next  to  the  coal-measure 
shales,  the  most  important  in  the  State.  According  to  Blatchley  (Ref. 
3)  the  Knobstone  shale  forms  the  surface-rock  of  a  strip  of  territory  3 


308 


CLAYS 


B.I 


g   a 

§ 


O      *4^j 

d   ~j 

If 


Longitude 


DISTRIBUTION   OF  CLAY  IN  THE  UNITED  STATES.  309 

to  38  miles  wide  on  the  eastern  side  of  the  Lower  Carboniferous  area, 
extending  from  the  Ohio  River  southwest  of  New  Albany  in  a  west  of 
north  direction  to  a  point  a  few  miles  south  of  Rensselaer,  Jasper  County. 

While  the  formation  is  often  covered  by  a  heavy  mantle  of  drift, 
many  excellent  exposures  have  been  formed  by  the  cutting  of  the  larger 
streams,  as  along  the  West  White  River  near  Martinsville;  along  Sugar 
Creek,  above  and  below  Crawfordville,  and  along  Shawnee  Creek  south 
of  Attica.  Many  additional  outcrops  have  been  found  in  other  counties 
within  the  belt  occupied  by  these  shales. 

The  Knobstone  formation  consists  of  blue-gray  shales,  shaly  sand- 
stones, and  sandstones,  with  rarely  a  little  limestone.  Nodules  of  sider- 
ite  are  not  uncommon. 

These  shales  are  utilized  at  New  Albany  for  stiff-mud  and  dry-press 
brick;  it  is  also  possible  that  they  could  be  used  for  sewer-pipe  when 
admixed  with  some  of  the  Carboniferous  under-clays. 


Carboniferous 

The  rocks  of  this  period  carry  the  most  valuable  clay-deposits  of  the 
State,  and  cover  an  area  of  about  7500  square  miles  in  14  counties  of 
western  and  southwestern  Indiana  (Fig.  51). 

They  form  part  of  a  large  basin,  underlying  western  and  southwestern 
Indiana  and  southern  Illinois,  so  that  those  in  Indiana  are  on  the  eastern 
edge,  and  therefore  dip  southwestward  and  westward.  This  being  so, 
the  lowest  rocks  of  the  section  outcrop  on  the  eastern  and  northeastern 
edge  of  the  area,  while  the  higher  lying  ones  outcrop  farther  westward. 

The  Carboniferous  rocks  consist  of  a  lower  member,  the  Mansfield 
sandstone,  and  an  upper  member,  the  coal-measures. 

Kaolin  or  indianaite. — At  the  base  of  the  Mansfield  sandstone  there 
is  a  thin  seam  of  coal,  which  is  replaced  at  a  number  of  localities  in 
Lawrence,  Martin,  and  Owen  counties  by  a  bed  of  kaolin  called  indiana- 
ite. 

Professor  Blatchley  states  that  "  Wherever  this  kaolin  is  found  it  is 
always  at  the  horizon  of  coal  I.  The  coal  and  kaolin  are  never  found 
at  the  same  place,  though  often  they  occur  but  short  distances  apart. 
At  Huron,  Lawrence  County,  where  the  best-known  deposit  is  located, 
the  kaolin  lies  in  a  horizontal  stratum  4  to  1 1  feet  in  thickness,  which  is 
overlain  by  a  sandstone,  and  in  places  contains  a  light-green  mineral 
known  as  allophane.  The  upper  half  of  the  kaolin  stratum  is  chiefly 
composed  of  massive  sno\v-white  clay  associated  with  which,  near  its 
MPP2F  part,  are  occasional  concretionary  masses,  some  of  them  a  foot 


310  CLAYS 

or  more  in  diameter.     These  disintegrate  on  exposure  to  air,  but  the 
kaolin  is  non-plastic. 

"An  analysis  of  the  kaolin  showed: 

Silica  (SiO2) 44.75 

Alumina  (A12O3) 38.69 

Water  (H2O) 15. 17 

Ferric  oxide  (Fe2O3) 95 

Lime  (CaO) 37 

Magnesia  (MgO) 30 

Potash  (K2O) 12 

Soda  (Na2O) 23 


100.58 

"  While  of  high  purity,  this  clay  is  not  now  used,  although  at  one  time 
it  was  made  into  alum  sulphate  for  sizing-paper." 

There  has  been  much  discussion  regarding  the  origin  of  this  kaolin, 
and  while  two  theories  have  been  advanced  to  explain  its  formation, 
both  acknowledge  its  residual  character,  and  that  of  the  inclosing  rocks, 
as  sedimentary. 

E.  T.  Cox  1  argued  that  the  kaolin  occupied  the  position  of  a  lime- 
stone bed,  and  that  carbonated  waters,  acting  on  the  latter,  replaced  the 
limestone  with  kaolinite.  Thompson  2  seconded  this  theory ,  but  added 
the  belief  that  the  surface-water  had  leached  the  alumina  and  silica 
from  the  overlying  sandstones. 

Lesquereaux,  on  the  other  hand ,  believed  that  the  kaolin  was  formed 
by  the  burning-out  of  coal-beds,  a  view  in  which  Ashley  concurred. 

Although  the  author  is  not  personally  acquainted  with  the  region,  it 
seems  to  him  that  there  are  certain  marked  objections  to  the  latter 
theory.  The  burning-out  of  the  coal  would  probably  produce  sufficient 
heat  to  cause  some  dehydration  of  the  kaolin,  whereas  there  is  no  evidence 
of  this.  In  just  what  \vay  the  kaolin  resembles  baked  fire-clay  is  not 
mentioned. 

It  is  not  necessary  to  suppose  any  complex  chemical  reactions  in 
order  to  derive  kaolin  from  limestone.  A  calcareous  rock,  containing 
aluminous  matter  very  low  in  impurities,  might  easily  yield  a  mass  of 
kaolin  by  simple  leaching,  and  residual  limestone  clays  of  rather  high 
purity  are  known  in  Missouri  and  also  Virginia. 

1  Sixth  Ann.  Rep.  Geol.  Surv.  of  Ind.,  1874,  p.  15. 

2  Ind.  Dept.  Geol.  and  Nat.  Hist.,  loth  Ann.  Rep.,  p.  37,  1886. 


DISTRIBUTION   OF  CLAY  IN  THE  UNITED  STATES 


311 


Coal-measure  clays  and  shales.  —  The  Coal-measures  include  a 
series  of  coals,  clays,  shales,  and  sandstones  (Fig.  52),  and  are  found  in 
a  number  of  counties  in  the  southwestern  part  of  the  State  (Fig.  51). 

Ashley  1  has  divided  them  vertically  into  eight  divisions  designated 
by  Roman  numerals,  these  divisions  being  based  on  the  position  of  some 
principal  coal-beds  or  horizons,  the  type  section  occurring  in  Clay  and 
Vigo  counties.  The  Mansfield  sandstone  found  in  general  along  the  east- 
ern edge  of  the  coal-field  forms  division  I,  and  the  main-worked  coals,, 
clays,  and  shales  occur  above  it  stratigraphically. 


-  Under 


Section  Near  Glen  Mine,  East  of  Coal  Bluff 


1.  Soil  and  surface  clay.  __  10 

2.  Potters.'  clay  ___________  1 

3.  CoalVb  ______________  1 

4.  Under-clay  ___________  8 

5.  Surface  soil  and  clay.  ____  0 

6.  Gravel  and  hard  pan..  ..20 

7.  Under-clay.  ____________  6 

8.  Gray  sandy  shale  ______  10 

9.  Gray  sandstone  _______  20 

10.  Coal  Va  _____________  l 

11.  Under-clay  ___________  8 

12.  Drab  clayey  shale  _____  14 

13.  Coal  V.  _______________  2 

14.  Under-clay.  ___________  n 

15.  Coal  IV.  _____________  4 

16.  Under-clay.  ___________  5+     0 


FIG.  52. — Section  near  Glen  Mine,  Coal  Bluff,  Ind.,  showing  association  of  coals , 
under-clays,  etc.  (After  Blatchley,  Ind.  Dept.  Geol.  and  Nat.  Res.,  29th 
Ann.  Kept.,  p.  183,  1905.) 

A  part  of  a  typical  vertical  section  showing  the  arrangement  of  the 
different  strata  of  the  coal-measures  and  their  relation  to  each  other 
is  given  by  Blatchley  (Ref.  3)  as  follows: 

Feet.  Inches. 

1.  Soil-  and  surface-clay 5  2 

2.  Sandstone,  massive  or  shelly 2  8 

3.  Blue  compact  shale 27  0 

4.  Coal  VII 4  10 

5.  Fire-clay 6  2 


Ind.  Dept.  Geol.  and  Nat.  Res.,  23d.  Ann.  Rept.,  1899. 


312  CLAYS 

Feet.  Inches. 

6.  Drab  siliceous  shale * 18          0 

7.  Limestone 3  8 

8.  Black  bituminous  shale 2  4 

9.  CoalVIfc 8 

10.  Fire-clay 5  6 

11.  Sandstone 13  0 

12.  Dark-gray  shale 11  2 

13.  Coal  VI 6  3 

14.  Hard  impure  bluish  fire-clay 11  0 

15.  Sandstone 21  0 

16.  Blue  limestone 11  0 

17.  Black  slaty  bituminous  shale 5  4 

18.  CoalV 5  2 

19.  Fire-clay 4  8 

The  fire-clays  (Nos.  5,  10, 14,  and  19)  are  almost  universal  accompani- 
ments of  the  overlying  coal-seams.  They  are  usually  one  to  six  feet 
thick,  and  are  a  soft  homogeneous  clay,  whitish  or  gray  in  color,  highly 
plastic,  and  often  of  excellent  refractoriness.  At  times,  however,  these 
under-clays  are  composed  of  a  hard,  bluish,  siliceous  clay  with  more  or 
less  pyrite  and  other  impurities. 

No.  14  is  of  this  character,  and  similar  clays  usually  occur  beneath 
coals  III  and  V,  but  those  below  coals  II,  IV,  VI,  and  VIII  are  often 
of  excellent  quality. 

The  blue,  gray,  and  drab  shales  (Nos.  3,  6,  and  12)  make  up  the 
greater  part  of  the  Coal-measure  rocks  of  Indiana,  and  include  the  most 
valuable  clay-deposits  found  in  the  State.  When  freshly  exposed  they 
are  usually  hard,  but  weather  down  easily  to  a  plastic  clay. 

The  relations  of  the  shales,  clays,  and  coal  are  such  that  the  three 
<;an  often  be  mined  by  one  shaft. 

The  coal-measure  clays  and  shales  are  worked  for  a  variety  of  purposes, 
including  pressed  and  paving  brick,  fireproofing,  sewer-pipe,  stoneware 
and  fire-brick. 

At  Brazil,  Clay  County,  which  is  a  most  important  clay-working  center, 
the  following  section  is  instructive. 

Feet.      Inches. 

1.  Soil  and  yellow  clay 12  0 

2.  Bowlder  clay,  blue 7  0 

3.  Gray  clayey  shale 33  0 

4.  CoalV 2  3 

5.  Under-clay  (potters'  clay) 3  2 

6.  Blue  clayey  shale 19  0 

7.  Bituminous  fossil  shale 1  6 

8.  Coal  IV 3  6 

9.  Under-cla-..  5  4 


DISTRIBUTION   OF   CLAY   IN   THE  UNITED   STATES  313 

No.  9  and  an  overlying  shale  are  used  for  sewer-pipe,  flue-linings, 
wall-coping,  etc.  No.  3  is  also  used  for  a  variety  of  purposes. 

The  best  deposits  of  unworked  shales  and  clays  for  making  vitrified 
bricks  lie  just  east  of  Mecca,  Parke  County;  west  of  Montezuma,  Parke 
County;  west  of  Terra  Haute,  and  near  Riley,  Vigo  County. 


Pleistocene  Clays 

These  are  soft,  plastic  clays,  found  at  the  surface  or  at  no  great 
distance  below  it,  and,  while  occurring  over  a  large  part  of  the  State,  they 
are  especially  important  in  the  northwestern  part  of  Indiana,  and  on 
this  account  have  been  made  the  subject  of  a  special  report.  (Ref.  1.) 

In  this  region  three  classes  are  distinguishable,  namely,  drift-clays 
or  "hard-pans,"  alluvial  clays,  and  silty  or  marly  clays. 

The  drift-clays  are  the  most  common  type,  forming  a  large  percentage 
of  the  unstratih'ed  morainic  material,  but  they  are  usually  too  impure 
and  calcareous  for  making  anything  but  common  brick  and  tile. 

The  alluvial  clays  form  larger  deposits  along  the  lowlands  and  second 
bottoms  of  the  large  streams  of  northwestern  Indiana,  having  been  formed 
during  periods  of  overflow,  and  in  some  places  showing  a  thickness  of 
30  to  90  feet. 

The  silty  or  marly  clays  resemble  those  of  the  preceding  class  very 
closely,  but  differ  in  having  been  deposited  in  bays,  lakes,  or  harbors 
in  quiet  water.  These  clays  are  usually  finer  grained  than  the  alluvial 
ones,  thinly  laminated,  and  often  highly  calcareous,  so  that  they  produce 
a  buff  product.  They  are  an  important  source  of  brick  and  tile  material 
in  Benton,  Newton,  Jasper,  Starke,  Lake,  Porter,  Laporte,and  St.  Joseph 
counties. 

In  other  parts  of  the  State  there  are  many  scattered  deposits  of 
surface-clays  used  for  brick  and  tile,  while  south  of  the  terminal  moraine 
in  southwestern  Indiana  there  are  many  deposits  of  loess  which  are 
available  for  the  same  purpose. 

The  analyses  on  page  314  are  given  by  Blatchley  (Ref.  3)  as  repre- 
sentative of  the  different  types  of  Indiana  clays  and  shales. 


References  on  Indiana  Clays 

1.  Blatchley,   W.   S.,   Clays   and   Clay   Industries   of   Northwestern 
Indiana,  Rept.  of  Indiana  State  Geologist  for  1897,  p.  106. 

2.  Blatchley,  W.  S.,  Preliminary  Report  on  the  Clays  and  Clay  In- 


314 


CLAYS 


dustries  of  the  Coal-bearing  Counties  of  Indiana,  Ind.  Dept.  of  Geol. 
and  Nat.  Res.,  20th  Ann.  Kept.,  p.  23,  1896. 

3.  Blatchley,  W.  S.,  The  Clays  and  Clay  Industries  of  Indiana,  Ind. 
Dept,  Geol.  and  Nat.  Res.,  29th  Ann.  Rept,,  pp.  13-658,  1904. 

4.  See  also  scattered  references  in  the  other  annual  reports  of  this 
survey. 

ANALYSES  OF  IXDIAXA  CLAYS 


I. 

II, 

III, 

IV. 

V 

VI. 

Silica  (SiO,) 

59  77 

58  83 

65  78 

67  65 

55  09 

83  44 

Alumina  (AlAO  
Ferric  oxide  (Fe2O3)  
Ferrous  oxide  (FeO)  
Lime  (CaO)  
Magnesia  (MgO)  
Potash  (KsjQ).  
Soda  (Na,O)  
Titanic  acid  (TiOL>)  
Carbon  dioxide  (CO,-),  etc  

20.60 
2.22 
3.70 
0.64 
1.98 
3.10 
0  85 
0.80 
0.90 

22  .  84 
5.13 
1.44 
0.49 
1.56 
4.18 
0.63 
0.70 

14.79 
8.03 

0.54 
1.42 
2.82 
0.97 
1.00 
0.26 

19.97 
0.72 

'6^48 
0.59 
1.75 
2.29 
1.01 
3  04 

20.76 
3.00 
4.01 
1.51 
1.18 
2.36 
0.34 
1.20 

10.36 
0.27 
0.28 
0.36 
0.14 
0  03 
0.71 
1.29 

Water  (HoO)  

4  .  53 

5  .  22 

4.98 

5.96 

7  01 

3  15 

VII. 

VIII. 

IX. 

X. 

XI. 

XII. 

Silica  (SiO->) 

69  23 

65  25 

59  64 

63  88 

70  eo 

€6  11 

Alumina  (Al..O3)  
Ferric  oxide  (Fe-O^).  .  .  . 

18.97 
1  57 

17.30 
2.30 

19.14 
3.39 

17.85 
5  38 

13.89 
2  83 

13.78 
5  35 

Ferrous  oxide  (FeO). 

0  55 

4  20 

3  56 

Lime  (CaO)  

0  12 

0.50 

0.26 

0  38 

0  CO 

1  67 

Magnesia  (MgO)  

0  36 

0.20 

2.31 

1  47 

0  £0 

1  78 

Potash  (K,O)  
Soda  (Xa26)  
Titanic  acid  (TiO.,)  
Carbon  dioxide  (CO.),  etc  
Water  (H,O)  

2.27 
0.33 
1.50 

5.46 

1.56 
0.98 

e'so 

5.40 

3.53 
0.80 
1.05 
0.35 
4.36 

3.98 
1.29 
0.91 

4*99 

2.76 
1.60 
0.43 
0.51 
3.19 

2.11 
1.15 

6^34 

XIII. 

XIV. 

XV. 

XVI. 

XVII. 

Silica  (SiO.) 

71    20 

72  56 

50  56 

50  47 

44  75 

Alumina  (AI.OO- 

18.56 

10  44 

13.11 

12  77 

38  69 

Ferric  oxide  (Fe-O  ).  .  .  . 

1  .34 

7.45 

2.98 

2  44 

0  95 

Ferrous  oxide  (FeO)  
Lime  (CaO)  
Magnesia  (MgO)  
Potash  (KoO).  

0.15 
0.14 
0.52 
0.32 

0  43 
0.82 
1.09 
2.05 

2.32 

7.87 
5.06 
3.74 

2.52 
8.17 
5.22 
3.70 

0'37' 
0.30 
0.12 

Soda  (Xa2O)  
Titanic  acid  (  TiO->) 

1.26 

0  88 

0.73 
0  31 

0.70 
1  00 

0.73 
1  45 

0.23 

Carbon  dioxide  (CO,)  etc 

9  62 

9  ,V0 

Water  (H-O) 

6  30 

4  54 

2  76 

3  14 

15.17 

DISTRIBUTION   OF  CLAY  IN   THE   UNITED  STATES 
RATIONAL  ANALYSES  OF  THE  PRECEDING 


315 


i. 

II. 

III. 

IV. 

V. 

Quartz                                     

26  .  04 

22.81 

34.34 

28.29 

20.90 

Feldspathic  detritus.  

8.37 

8  30 

12  58 

34.77 

2.03 

Ferrous  carbonate  

2.37 

6.46 

Magnesium  carbonate 

0  50 

1  13 

Clay  substance       

63.22 

68.89 

52.58 

36  .  94 

69.48 

VI. 

VII. 

IX. 

X. 

XL 

46  33 

39  36 

25  57 

17  93 

56  65 

Feldspathic  detritus 

39  28 

1   67 

6  86 

42  03 

16  63 

Ferrous  carbonate 

1  07 

Magnesium  carbonate.       .  . 

0  67 

0  08 

Clay  substance 

14  39 

58  37 

66  90 

40  04 

25  57 

LOCALITIES  OF  THE  PRECEDING 


No. 

Location. 

Geological  Age. 

I. 

II. 
III. 
IV. 
V. 
VI. 
VII. 
VIII 
IX. 
X. 
XI. 
XII. 
XIII. 
XIV 
XV. 
XVI. 
XVII. 

Mecca,  Mecca  Coal  and  Mining  Company  

Cayuga,  Cayuga  Brick  and  Coal  Company.  .  .  . 
Mecca,  Mecca  Coal  and  Mining  Company  
Cayuga,  Cayuga  Brick  and  Coal  Company.  .  .  . 
W    Montezuma    Burns  &  Hancock 

Carboniferous  shale 

<  «                t 

<  <                « 

Coal-measures  under-clay 

n             1  1             (       1  1 

(  t                          fC                           (              11 

It                ((                <         t  ( 
<  e                   t  <                    i          1  1 

Knobstone  shale 

(  (                         <  C 

(I                  (I 

Alluvial 
Surface  Loess 
Residual 
Pleistocene 
Pleistocene 
Residual 

Huntingburg,  Bockting  Bros  

Huntingburg   C    Fuchs.  . 

Blue  Lick 

New  Albany 

Martinsville    Branch  &  Sons  . 

Terre  Haute. 

Princeton 

Four  miles  south  of  Bloomington              .    . 

Hobart                                                    .  .  . 

Michigan   . 

Indianaite   Huron   Dr  Gardner.  . 

Indian  Territory  1 

The  greater  part  of  the  Cherokee  and  Creek  nations  and  the  northern 
part  of  the  Choctaw  nation  contains  extensive  deposits  of  clays  of  Penn- 
sylvanian  age,  which  are  very  similar  to  the  brick-  and  tile-clays  of  south- 
eastern Kansas,  and  the  presence  of  gas  in  that  region  will  warrant  the 
development  of  extensive  industries.  In  the  western  part  of  the  Chicka- 
saw  nation  the  country  is  underlain  with  red  clay  of  the  Permian  red 


From  note  supplied  by  Professor  C.  N.  Gould. 


316  CLAYS 

beds,  the  same  as  that  found  in  Oklahoma,  while  in  the  southern  part  of 
the  Choctaw  and  Chickasaw  nations  the  clay  is  of  Lower  Cretaceous  age, 
similar  to  that  in  central  Texas. 

Probably  the  best  clay  in  Indian  Territory  so  far  discovered  is  from 
the  formation  known  as  Sylvan  Shale  of  Silurian  age,  which  outcrops 
in  various  places  in  the  Arbuckle  Mountains  in  the  eastern  part  of  the 
Chickasaw  nation.  A  company  is  now  engaged  in  developing  the  clay- 
products  at  Oolite,  where  plants  are  being  erected  for  the  manufacture 
of  brick,  tile,  sewer-pipe,  fireproofing,  and  cement. 

Iowa 

Every  great  rock  formation  of  Iowa,  except  one,  the  Sioux  quartzite 
contains  more  or  less  important  clay-  or  shale-deposits,  but  the  different 
ones  represent  a  wide  range  of  structural  characters  and  physical  or 
chemical  properties,  these  variations  occurring  sometimes  within  the 
same  formation. 

Cambrian 

Saint  Croix  sandstone. — This  carries  a  few  shale-beds  which  outcrop 
in  portions  of  Allamakee  and  Clayton  counties,  but  nothing  is  known 
regarding  their  economic  value. 

Ordovician 

Galena-Trenton. — Although  essentially  a  limestone  formation,  this 
nevertheless  contains  a  few  beds  of  shale,  which  may  be  adaptable  to 
pottery  manufacture.  The  best  exposure  is  on  Silver  Creek,  Makee 
township,  Allamakee  County.  Concretions  and  fossils  are  apt  to  render 
this  shale  worthless. 

Maquoketa  shale. — This,  the  oldest  shale  formation  of  importance 
in  the  State,  forms  a  narrow,  sinuous  band  from  Jackson  County  on 
the  south  to  Winneshiek  and  Howard  counties.  The  shale  is  divisible 
into  two  groups,  the  upper  consisting  of  a  plastic  clay,  with  occasional 
limestone  layers,  while  the  lower  is  of  lean  fissile  shales,  with  some  earthy, 
fossiliferous  beds.  They  are  mostly  red-burning,  but  may  at  times 
be  quite  calcareous,  and  though  their  chief  use  is  for  common  brick, 
they  have  also  given  excellent  results  for  earthenware  manufacture 
and  hollow  brick. 

Silurian 

The  beds  of  this  system  are  practically  devoid  of  shale-deposits. 


DISTRIBUTION  OF  CLAY  IN  THE  UNITED  STATES 


317 


318  CLAYS 


Devonian 

The  lower  argillaceous   beds,   known   as   the  Independenc 
outcrop  in  limited  measure  in  Cedar,  Linn,  and  Buchanan  counties,  but 
are  of  no  economic  importance. 

The  upper  shales,  which  are  typically  developed  along  Lime  Creek 
in  Cerro  Gordo  and  Floyd  counties,  and  at  Rockford  and  Mason  City 
are  of  much  greater  value.  Owing  to  a  variable  lime-content  the  clays 
burn  either  light  red  or  cream,  but  in  either  case  have  yielded  good  results 
in  the  manufacture  of  common  and  hollow  brick  and  drain-tile.  The 
shales  are  too  fusible  to  take  a  salt-glaze. 

Carboniferous 

Practically  all  of  the  great  formations  of  the  Carboniferous  contain 
clays  of  importance,  but  those  of  the  Kinderhook  and  Coal-measures  are 
especially  important.  According  to  Beyer  and  Williams,  "Rocks  referable 
to  the  Carboniferous  comprise  the  indurated  rocks  over  nearly  one  half 
of  the  surface  of  the  State.  The  system  may  be  divided  into  two  parts: 
(1)  the  Lower  Carboniferous  beds,  which  are  prevailingly  calcareous  in 
character,  and  (2)  the  Upper  Carboniferous,  in  which  arenaceous  and 
argillaceous  deposits  predominate,  with  important  limestone  bands  in 
the  upper  portion.  The  latter  division  contains  all  of  the  workable  coal 
in  the  State.  On  account  of  the  abundance  of  raw  material  suitable 
for  the  manufacture  of  clay  wares  and  cheap  fuel,  the  Upper  Carbon- 
iferous or  Coal-measures  constitute  the  most  important  formation  to 
the  clay-worker  in  the  State. 

"The  Lower  Carboniferous  comprises  a  belt  averaging  from  thirty 
to  forty  miles  in  width,  and  extending  diagonally  across  the  State  from 
Kossuth  and  Winnebago  counties  on  the  north  to  Des  Moines  and  Lee 
counties  on  the  south.  Narrow  strips  have  been  laid  bare  by  the  lower 
courses  of  the  Skunk  and  Des  Moines  rivers,  and  unimportant  detached 
areas  appear  in  Story  and  Webster  counties.  Three  stages  represent 
the  Lower  Carboniferous  in  Iowa,  namely,  the  Kinderhook,  Augusta, 
and  Saint  Louis." 

Kinderhook. — The  shales  of  this  formation  are  specially  prominent 
in  Des  Moines  and  Lee  counties;  they  are  red- or  brown-burning  and  used 
for  common  brick. 

Augusta. — These  shales  are  of  little  importance  except  in  Lee  County, 
and  even  there  are  rather  calcareous. 


PLATE  XXVII 


FIG.   1. — Carboniferous  shale  for  paving-blocks  near  Veedersburg,  Ind.      (After 
Blatchley.  29th  Ann.  Rep.,  Ind.  Dept.  Geol.  and  Nat.  Res.,  p.  80.) 


FIG.  2. — Cretaceous  shale,  Sioux  City,  la.     (After  Williams,  la.  Geol.  Surv., 
XIV,  p.  518,  1904  ) 

319 


DISTRIBUTION   OF  CLAY  IN  THE  UNITED  STATES  321 


Coal-measures 

The  rocks  of  this  age  cover  nearly  one  third  of  the  State  and  carry 
a  great  range  of  argillaceous  beds  grouped  as  (1)  argillaceous,  (2)  arena- 
ceous, (3)  carbonaceous  or  bituminous,  and  (4)  calcareous  varieties. 
These  grade  into  each  other  both  vertically  and  horizontally.  Although 
the  coal-measures  are  present  in  ninety-nine  counties  of  the  State,  the 
clay-shales  are  utilized  for  making  clay-products  in  but  sixteen.  The 
argillaceous  shales  are  often  found  underlying  the  coal-seams,  and 
are  not  uncommonly  of  refractory  character,  but  the  calcareous  ones 
contain  too  much  limey  matter  to  be  of  great  value.  Those  beds 
of  the  Coal-measures  prominent  along  the  Des  Moines  River  'contain 
argillaceous,  bituminous,  and  arenaceous  shales,  while  in  the  beds 
most  prominent  along  the  Missouri  River  the  calcareous  members  are 
more  prominent. 

It  is  difficult  to  generalize  regarding  the  clays  of  this  series,  but  at 
any  one  point  it  is  not  uncommon  to  find  several  grades  of  clay  ranging 
from  common  brick-clay  to  fire-clay  in  the  same  section.  The  shales  are 
worked  at  a  number  of  points,  among  which  Van  Meter,  Dallas  County; 
Des  Moines,  Polk  County;  Ottumwa,  Wapello  County;  and  Fort  Dodge, 
Wapello  County  may  be  mentioned.  The  clays  are  worked  either  as 
open  pits  or  undergound  mining  and  the  products  include  common  and 
pressed  brick,  paving-brick,  hollow  blocks,  drain-tile,  stoneware,  and 
fire-bricks.  Analyses  of  these  are  given  on  a  later  page. 


Cretaceous 

The  Cretaceous  of  Iowa  consists  of  a  lower  sandstone  and  shale 
series,  the  Dakota,  and  an  upper  series  of  interbedded  sandstones, 
shales,  and  marly  limestones.  These  rocks  cover  approximately  the  north- 
western third  of  the  State,  shale-beds  of  this  age  being  known  in  Sioux 
(PL XXVII, Fig. 2), Plymouth,  Woodbury,  Sac, Calhoun, and  Montgomery 
counties. 

The  shales  show  about  the  same  textural  and  chemical  range  as  the 
Carboniferous  ones,  but  on  the  whole  are  more  siliceous. 

At  Red  Oak,  Montgomery  County,  both  white  stoneware  and  fire-brick 
are  made,  and  it  has  been  suggested  that  washing  might  render  the 
clay  available  for  glass-pot  manufacture.  Other  products  from  these 
shales  are  paving  and  common  brick. 


322  CLAYS 


Pleistocene 

Covering  all  of  the  State,  with  the  exception  of  a  small  area  in  the 
northeastern  corner,  is  a  thick  mantle  of  glacial  deposits  which  range 
in  thickness  from  zero  up  to  three  or  four  hundred  feet.  The  glacial 
drift  is  composed  of  a  heterogeneous  mass  of  bowlder  beds,  gravel,  and 
sand-deposits,  and  more  rarely  beds  of  clay,  which,  owing  to  a  natural 
washing  process  which  they  have  undergone,  are  sufficiently  plastic  to 
be  molded  into  clay  wares.  They  often  suffer,  however,  from  the  presence 
of  lime  pebbles  or  stones,  and  even  if  free  from  these  are  still  unsatisfac- 
tory because  of  their  high  shrinkage,  which  causes  a  loss  due  to  checking 
in  drying  and  burning.  A  few  of  the  drift-sheets,  however,  contain 
clays  of  satisfactory  character  for  brick  manufacture. 

Loess. — Associated  with  the  drift-sheets  and  of  far  greater  economic 
importance  are  the  massive  structureless  deposits  of  loess.  (PI.  XXVIII, 
Fig.  1.)  These  consist  of  clays  or  clayey  silts,  which  form  a  mantle  over 
about  two  thirds  of  the  area  of  the  State,  affording  an  inexhaustible 
supply  of  brick  material. 

This  occurs  beyond  the  borders  of  the  drift-sheets  and  even  over- 
lapping them.  It  covers  more  than  one  half  the  surface  of  the  State 
and  shows  great  irregularity  in  thickness,  being  over  one  hundred  feet 
thick  along  the  Missouri  River.  It  affords  an  exhaustless  supply  of 
material  suitable  for  the  manufacture  of  brick  by  the  soft-mud,  stiff- 
mud,  or  dry-press  process,  and  moreover  is  a  very  cheap  clay  to  work. 

Of  the  several  types  of  loess  recognized  in  the  State,  the  "gumbo" 
is  noteworthy.  This  is  a  thoroughly  oxidized  and  leached  red  clay  which 
on  drying  breaks  up  into  a  number  of  angular  fragments.  In  the 
southern  part  of  the  State  the  gumbo  is  gray  or  drab  in  color.  Its 
peculiarity  is  its  excessive  shrinkage  which  precludes  its  use  for  the 
manufacture  of  brick,  but  makes  it  admirably  adapted  to  the  manufacture 
of  burned-clay  ballast. 

The  chemical  composition  of  a  number  of  representative  Iowa  clays 
and  shales  is  given  in  the  table  on  page  325. 

References  on  Iowa  Clays 

1.  Beyer,  S.  W.,  Origin  and  Classification  of  Iowa  Clays,  Clay  Record, 
XX,  No.  3. 

2.  Beyer,  Weems  and  Williams,  The  Clays  of  Iowa,  la.  Geol.  Surv., 
XIV,  1904. 


PLATE  XXVIII 


FJG.  1. — Loess-bank,  Muscatine,  la.     (After  Williams,  la.  Geol.  Surv.,  XIV,  1904.) 


FIG.  2.— Bank  of  (Devonian)  shale  used  for  paving-brick,  Cumberland,  Md. 
H.  Ries,  Md.  Geol.  Surv.,  IV,  p.  454,  1902.) 

323 


(After 


DISTRIBUTION  OF  CLAY  IN  THE  UNITED  STATES 


325 


3.  Youtz,  L.  A.,  Clays   of  the   Indianola  Brick,  Tile,  .and  Pottery 
Works,  la.  Acad.  Sci.  Proc.,  Ill,  p.  40,  1896. 


ANALYSES  OF  IOWA  CLAYS 

ULTIMATE    ANALYSES 


I. 

II. 

III. 

IV. 

V. 

VI. 

VII. 

VIII. 

Silica  (SiO2)  

67.50 

61.59 

73.43 

63.78 

58.56 

75.85 

58  05 

77  39 

Alumina  (A12O3)  
Ferric  oxide  (Fe2O3).  .  .. 
Lime  (CaO)  ;.. 
Magnesia  (MgO)  

15.75 
4.80 
2.57 
1.57 

21.01 
4.72 
3.58 
2  16 

11.94 
3.83 
1.00 
0  86 

19.78 

l!55 
1.22 

22.33 
2.87 
3.60 
1.44 

10.73 
1.43 
1.00 
0  49 

23.05 
3.83 
0.30 
2  04 

5.16 
2.40 
3.65 
3  13 

Potash  (K2O)  
Soda  (Na2O)  .  ... 

0.95 
1.56 

0.52 
1   13 

0.05 
0.95 

0.54 
1.20 

i!os 

0.24 
0.70 

0.90 
2  04 

1.44 
2  79 

Comb,  water  (H2O).  .  .  . 
Carbon  dioxide  (CO2).  . 

Sulphur  trioxide  (SO3).  . 
Moisture  

3.22 
with 
noist. 
with 
moist. 
2.88 

4.51 

0.95 
0.4? 

4.33 
0.90 

1.65 
0.63 

2.92 
with 
moist, 
with 
moist. 
3.88 

7.11 
with 
moist, 
with 
moist. 
2.98 

6.38 
with 
moist, 
with 
moist. 
3  18 

8.1G 

0.86 
0  96 

1.46 

1.44 
0  13 

IX. 

X. 

XI 

XII. 

XIII. 

XIV. 

XV. 

XVI. 

Silica_(SiO2)  
Alumina  (A12O3)  
Ferric  oxide  (Fe2O3).  .  . 
Lime  (CaO)  

58.33 
15.54 
3.84 
9.42 

47.40 
22.20 
12.40 
0.70 

28.82 
10.37 
3.76 
19.14 

66.44 
12.64 
4.00 
4.02 

51.95 
18.34 
7.56 
4.14 

44.39 
13.72 

7.80 
7  88 

68.22 
10.21 

2.87 
3  90 

67.92 
11.76 
6.72 
1  63 

Magnesia  (MgO)  
Potash  (K2O).  

3.03 
1.19 

1.10 
3.10 

5.40 
5.38 

1.80 
1.14 

3.26 
1.43 

6.05 
1.56 

3.16 
0  58 

1.18 

1  87 

Soda  (Na2O)  

1.76 

0.50 

7.41 

1.90 

2.69 

5.29 

1  68 

1  92 

Comb,  water  (H2O)..  .  . 
Carbon  dioxide  (CO2) 

3.47 
2  02 

7.90 

16.24 

5.83 

7.3C 

12.18 

1.52 
5  86 

5.36 

Sulphur  trioxide  (SO3).. 

1.10 

2.40 

3.01 

2.76 

1.45 

Moisture 

0  42 

2  10 

0  43 

2  33 

0  42 

0  89 

0  62 

1  49 

RATIONAL   ANALYSES 


I. 

II. 

III. 

IV. 

V. 

VI. 

VII. 

VIII. 

Clay 

52.85 

56.79 

41.47 

61.57 

57.40 

38.20 

68.20 

24  92 

Quartz       

25.99 

19.63 

55.29 

20.53 

31.17 

51.10 

25.81 

51.39 

Feldspar 

15  80 

21  96 

3  24 

13  47 

4  38 

7  62 

5  99 

19  64 

Carbonates      and     sul- 
phates of  Ca  +  Mg. 

5  36 

1.62 

4  43 

7  05 

3  08 

4  05 

IX. 

X. 

XI. 

XII. 

XIII. 

XIV. 

XV. 

XVI. 

Clay.              

64.47 

74.90 

68  .  20 

38.80 

47.08 

40.61 

19  72 

39  90 

Quartz 

18  67 

12  70 

21  75 

36  36 

41  45 

28  00 

40  29 

40  28 

Feldspar 

11   13 

8  81 

4  98 

24  84 

6  98 

4  62 

25  74 

19  82 

Carbonates      and     sul- 
phates of  Ca  +  Mg   .  . 

5  73 

3  5f 

5  12 

4  49 

26  77 

14  25 

326 


CLAYS 


LOCALITIES  OF  THE  PRECEDING 


No. 


Locality. 


Geological  Age. 


Uses. 


I 
II 

III 

IV 

V 

VI 

VII 

VIII, 

IX. 

X. 

XL 

XII. 

XIII. 

XIV. 

XV. 

XVI. 


Flint  Brick  Co.,  Des  Moines. , 
Iowa  Brick  Co.,  Des  Moines  , 


Flint  Brick  Co.,  Des  Moines 

Capital  CityBrick  Co., Des  Moines 
J.  Holman,  Sargent's  Bluff 

Corey  Pr.  Br.  Co.,  Lehigh 


Granite  Br.  Co.,  Cascade 

Cream  City  B.  &  T.  Co.,  Rockford 
Boone  Br.  &  T.  Co.,  Boone 


Clermont 

Storm  Lake.  . 
Mason  City.  . . 
Edge  wood.  .  .  . 
Council  Bluffs. 


Gladbrook. 


Coal-measures 


n          it 
Cretaceous 

Coal-measures 

Kinderhook 

Devonian 

Coal-measures 

Maquoketa 
Drift 
Devonian 
Maquoketa 
Loess  (Mo.) 

Inland  Loess 


Paving-  and  building-brick 

Paving-brick,  builders,  and 
hollow  ware,  bottom 

Ditto,  top 

Paving-brick;  green-brick 
mixture 

Brick  and  tile 

Common,  face,  paving- 
brick,  sidewalk  brick 

Pressed  face  brick  and  or- 
mentals 

Common  and  paving  brick 

Brick  and  tile 

Paving,  hollow  ware,  com- 
mon brick 

Brick  and  tile 

Drain -tile 

Brick  and  tile 

Brick  and  tile 

Soft-mud,  stiff-mud,  and 
pressed  brick 

Pressed  brick 


These   analyses  are  all  from  Vol.  XIV,  la.  Geol.  Surv.,  and  have    been  kindly  selected  as 
representative  by  Professor  I.  A.  Williams. 


Kansas 

This  State  probably  contains  an  abundance  of  clays  of  low  and  medium 
grade,  but  they  have  not  as  yet  been  systematically  investigated.  The 
formations  yielding  them  are  of  Carboniferous,  Permian,  Triassic,  Cre- 
taceous, Tertiary,  and  Pleistocene  age. 


Carboniferous 


The  Coal-measures  underlie  a  rather  extensive  area  in  eastern  Kansas, 
and  consist  of  alternating  strata  of  limestones,  shales,  and  sandstones, 
with  occasional  coals.  These  beds  dip  gently  to  the  westward,  so  that 
any  one  bed  passes  under  the  overlying  ones  if  traced  in  that  direction. 

The  shales  of  this  series  are  mostly  red-burning  and  at  different 
localities  have  been  found  adapted  to  the  manufacture  of  common 
and  pressed  brick,  drain-tile,  vitrified  brick,  and  more  recently  even  for 
roofing-tile  and  stoneware.  They  were  first  worked  at  Atchison  in 
1887,  but  since  then  factories  have  been  opened  up  at  Topeka,  Pittsburg, 
Chanute,  Coffeeville,  etc.  Those  at  Cherryvale  are  found  immediately 


DISTRIBUTION  OF  CLAY  IN  THE   UNITED  STATES  327 

underlying  the  Independence  limestone,  while  the  beds  worked  at  lola 
overlie  the  lola  limestone.  At  Lawrence  the  beds  utilized  occupy,  a 
position  near  the  middle  of  the  Lawrence  shales  and  right  under  the 
Oread  limestone. 

The  coal-measure  shales  of  southeastern  Kansas  are  ideally  located, 
because  of  the  supply  of  natural-gas  fuel.  The  Permian  outcrops  to 
the  west  of  the  coal-measures  being  found  particularly  in  the  Flint  Hills 
area,  and  Haworth  states  that  the  shales  are  purer  than  those  of  the 
coal-measures. 

Triassic 

These  occur  in  abundance,  as  at  near  Kingman,  and  Prosser  states 
that  they  have  been  used  for  paint. 


Cretaceous 

The  Dakota  shales  are  well  exposed  near  Salina,  Dickinson  County, 
but  so  far  as  known  have  not  been  utilized  to  any  extent. 


Pleistocene 

The  surface-clays  are  widely  distributed  over  Kansas,  but  are  chiefly 
important  in  the  eastern  portion.  The  gumbo  clay,  dug  in  many  of  the 
river  valleys  has  been  burned  in  large  quantities  for  railroad  ballast. 


References  on  Kansas  Clays 

1.  Grimsley,  G.  P.,  Kansas  Mineral  Products,  Eleventh  Bien.  Rept., 
Kas.  Board  of  Agric.,  1897-98,  p.  507,  1898. 

2.  Haworth,  E.,  Annual  Bulletins  on  Mineral  Resources  of  Kansas, 
issued  by  Univ.  Geol.  Survey,  as  follows:  1899,  p.  57;    1900  and  1901, 
p.  60;    1902,  p.  40;    1897,  p.  81;    1898,  p.  61. 

3.  Hay,  R.,  Geology  and  Mineral  Resources  of  Kansas,  Eight  Bien. 
Rept.,  State  Agric.  Board,  1891-92,  p.  54,  1893. 

4.  Prosser,  C.  S.,  Clay-deposits  of  Kansas,  U.  S.  Geol.  Surv.,  Min. 
Res.  for  1892,  p.  731,  1394. 

5.  Schrader,  F.  C.,  and  Haworth,  E.,  Clay  Industries  of  the  Indepen- 
dence District,  U.  S.  Geol.  Surv.,  Bull.  260,  p.  546,  1905. 


328  CLAYS 


Kentucky 

The  clays  of  this  State,  like  those  of  many  others,  have  never  been 
systematically  investigated,  although  the  former  Kentucky  Geological 
Survey  published  a  large  number  of  analyses.1  A  great  many  scattered 
notes  and  short  articles  are  also  found  in  the  various  reports,  from  which 
the  following  are  largely  taken. 

Within  the  State  there  are  found  a  series  of  geologic  formations 
ranging  from  the  Ordovician  to  the  Pleistocene.  Some  of  these  con- 
tain deposits  of  soft,  plastic  clays  or  shales,  while  others  yield  clays  only 
as  a  result  of  surface-weathering.  A  section  across  the  State  from  east 
to  west  shows  that  the  formations  are  not  highly  tilted  as  they  are 
farther  eastward,  but  that  they  are  rather  flat,  having  a  comparatively 
gentle  dip,  so  that  in  any  one  area  where  two  formations  are  exposed 
the  older  of  the  two  may  have  been  laid  bare  as  the  result  of  erosion. 


Ordovician-Devonian 

The  Ordovician,  Silurian,  and  Devonian  formations  occupy  a  some- 
what circular  area  in  central  and  north-central  Kentucky.  They  con- 
tain a  series  of  shales,  limestones,  and  sandstones,  the  first  of  which  are 
usually  calcareous,  and  probably  of  little  value  except  for  common- 
brick  manufacture;  but  nearly  all  of  these  formations  yield  residual 
clays  which  are  mostly  of  low  lime-content  and  generally  high  in  iron. 
They  are  used  for  common-brick  manufacture,  and  those  at  Waco  are 
stated  to  be  of  value  for  pottery.2 

Carboniferous 

Lower  Carboniferous. — The  beds  of  this  age  are  found  in  both  the 
eastern  and  western  parts  of  the  State  and  include  several  deposits  of 
shales  and  clays,  which  to  judge  from  the  published  analyses  are  of  low 
fusibility  and  of  red-burning  character. 


1  Ky.  Geol.  Surv.,  Chem.  Analyses,  A,  Pts.  I,  II,  and  111. 

2  For  Ordovician,  see  Ky.  Geol.  Surv.,  reports  on  Oldham  County,  p.  19;  Kenton 
County,  p.  133;   Jefferson  County,  p.  50;   and  Chem.  Analyses,  Pt.  I,  1884,  pp.  34 
and  76.     For  Silurian,  consult  Ky.  Geol.  Surv.,  new  series,  III,  p.  156;    Chem. 
Analyses,  Pt.  I,  pp.  83,  130,  and  288;   Fleming  County,  p.  70;   Clark  County  p.  28. 


DISTRIBUTION   OF  CLAY  IN   THE   UNITED  STATES  329 

Coal-measures. — The  coal-measure  beds  will  undoubtedly  be  found 
to  contain  the  most  valuable  clays  of  the  State,  arid  all  of  the  high- 
grade  fire-clays  thus  far  dug  in  Kentucky  have  been  obtained  from 
them.  They  occur  in  both  the  eastern  arid  western  portions  of  the 
State,  in  the  coal-fields,  but  the  beds  have  not  been  systematically 
traced  or  tested. 

In  the  eastern  field  a  fire-clay  is  said  to  occur  near  the  base  of  the 
subconglomerate,  but  is  lacking  in  persistence.  This  is  said  to  correspond 
to  the  fire-clay  worked  at  Sciotoville,  Ohio,  and  is  found  in  Greenup, 
Boyd,  Carter,  and  Lawrence  counties;  indeed,  it  is  reported  to  have 
been  shipped  in  large  quantities  from  Indian  Run  in  Greenup  County. 
Clay  of  high  refractoriness  is  obtained  near  Olive  Hill  and  molded  for 
fire-brick. 

Fire-clay  is  also  stated  to  accompany  many  of  the  coal-seams  in 
parts  of  Jackson,  Pulaski,  and  Rockcastle  counties.1 

The  upper  Ferriferous  Limestone  contains  a  bed  of  ore,  usually 
overlain  by  a  fire-clay,  in  Greenup,  Carter,  and  Boyd  counties,  it  has 
been  worked  for  fire-brick  at  Bellefonte,  and  also  for  pottery  near 
Cincinnati.2 

In  the  western  coal-field  fire-clays  are  known  to  occur,  but  there  is 
little  available  information  regarding  them.  Vitrified  brick-clay  is  worked 
at  Cloverport  in  Grayson  County. 


Tertiary 

Tertiary  clays  of  sandy  to  highly  plastic  character,  and  often  of  good 
refractoriness,  occur  at  a  number  of  points  in  the  extreme  western  part 
of  the  State,  while  ball-clay  has  been  dug  in  large  quantities  from  the 
area  around  Mayfield.3 

Recent  Clays 

Alluvial  deposits  suitable  for  making  common  brick  are  to  be  looked 
for  along  many  of  the  river  valleys. 

The  analyses  shown  on  page  330  are  selected  from  the  published 
reports  of  the  Kentucky  Geological  Survey. 

•See  Ky.  Geol.  Surv.,  Eastern  Coal-field,  1884,  pp.  30,  32,  33,  43,  201;  also 
U.  S.  Geol.  Surv.,  Geol.  Atlas,  Folio  47,  London  sheet. 

2  Ky.  Geol.  Surv.,  Eastern  Coal-field,  pp.  140  and  141. 

3  U.  S.  Geol.  Surv.,  Prof.  Pap.  11,  p.  39,  1903. 


330 


CLAYS 


References  on  Kentucky  Clays 

1.  Crump,   H.   M.,   The  Clays   and   Building   Stones   of   Kentucky, 
Eng.  and  Min.  Jour.,  LXVI,  p.  190,  1898. 

2.  Many  reports  of  Ky.  Geol.  Surv.,  for  summary    of    which    see 
U.  S.  GeoL  Surv.,  Prof.  Pap.  No.  11,  1903. 

3.  Reports  of  Ky.  Geol.  Surv.,  Chemical  Analyses,  A,  Pts.  1,  11,  and 
III,  contain  many  analyses. 

4.  Ky.  Geol.  Surv.,  Kept,  on  Jackson-Purchase  Region,  deals  chiefly 
with  the  Tertiary  clays. 

ANALYSES  OF  KENTUCKY  CLAYS 


i. 

II. 

III. 

IV. 

V. 

VI. 

Silica  (SiO2)  .  . 

56  40 

59  97 

63  12 

61  10 

46  56 

43  58 

Alumina  (Al.Os)  1 

18.20 

37.47 

40  86 

Ferric  oxide  (Fe2O3)   .    .           J 

29.97* 

27  .  64* 

8.56 

6  00 

trace 

0  76 

Lime  (CaO)  . 

6  26 

4  90 

0  112 

0  29 

Magnesia  (MgO).  . 

1  51 

0  60 

2  03 

1  54 

trace 

0  14 

Potash  (K2O). 

3  53 

3  93 

1  36 

4  10 

0  28 

0  19 

Soda  (Na2O).      .            ... 

0  55 

0  54 

0  82 

0  28 

0  05 

Phosphoric  acid  (P2O-)  

0.16 

with 

0  14 

0  25 

Loss  on  ignition  

7.10 

Al,03 
7.02 

12  00 

3  33 

13  03 

14  43 

Lime  carbonate  (CaCO3)  

0.76 

0.28 

VII. 

VIII. 

IX. 

X. 

XI. 

XII 

Silica  (SiO2">  • 

62  92 

47  56 

84  76 

40   14 

£A   44 

or:    10 

Alumina  (A12O3),  
Ferric  oxide  (Fe2O3) 

20  '73 
3  82 

40.66 
trace 

}  11.40 

43.72 
1  98 

128.00 

10.26 
1   12 

Lime  (CaO)   . 

0  21 

0  28 

trace 

) 

trace 

Magnesia  (MgO)  . 

0  13 

0  49 

0  65 

\    1  60 

1.30 

0  06 

Potash  (K2O).     . 

0  19 

0  30 

1  58 

0  95 

Soda  (Na2O).      . 

0  21 

0  40 

0  05 

0  14 

Phosphoric  acid  (P2O5)  
Sulphur  trioxide  (SO3)  

0.62 
undet 

0.24 
trace 

12.56 

14.30 

Loss  on  ignition  

13  66 

10  03 

1  56 

J 

2  27 

XIII. 

XIV. 

XV. 

XVI. 

XVII. 

XVIII. 

Silica  (SiO2)  

74  10 

61  68 

56  98 

62  68 

75  55 

59  50 

Alumina  (A12O3)  

16  46 

28  50 

32  16 

25  88 

16  75 

24  96 

Ferric  oxide  (Fe2O3)  

2  70 

1  68 

2  16 

2  90 

1   19 

0  72 

Lime  (CaO)  . 

0  35 

0  10 

0  32 

Magnesia  (MgO).  . 

0  18 

0  13 

0  20 

0  31 

0  14 

0  39 

Potash  (K2O). 

0  55 

1   15 

0  83 

1   14 

1  09 

1  93 

Soda  (Na2O)       .    . 

0  13 

0  82 

0  11 

0  92 

0  21 

0  28 

Loss  on  ignition  

5  50 

5  92 

7  54 

6  14 

5  04 

11  87 

Includes  MnO. 


DISTRIBUTION   OF  CLAY   IN    THE   UNITED   STATES 


331 


LOCALITIES  OF  THE  PRECEDING 


No. 


1. 

II. 
111. 
IV. 

V. 
VI. 

VII. 

via. 

IX. 
X. 

XI. 

XII. 

XIII. 

XIV. 

XV. 

XVI. 

XVII. 

XVIII. 


Location 


Two  miles  south  of  Covington 
Waco.  . 


Nelson  County 

Boone  Furnace 

Perry's    branch,    Tygart     Creek,     near 

E.  L.  &B.  S.  R.  R 

Two  miles  from  Ken  ton  Furnace 

Wing's  branch,  Shultz  Creek 

Whitley  County 

Ashland  (used) 


Columbus 

Hickman's  Bluff 

Three  miles  east  of  New  Providence. 

Bell  City 

Six  miles  east  of  Mayfield 

Wickliffe 

Four  miles  south  of  Paducah .  . 


Geological  Age. 


Cincinnati  group  Lower  Silurian 
Upper  Silurian 
''Ohio"  Devonian  shale 
Keokuk,  Lower  Carboniferous 
Coal-measures 


Tert  ary 


Louisiana 

• 

The  workable  clays  of  Louisiana  (Ref .  1)  are  all  of  transported  char- 
acter and  post-Tertiary  age.  Three  distinct  types  of  clay  are  worked  in 
Louisiana,  and  each  of  these  is  characteristic  of  that  portion  of  the 
State  in  which  it  occurs. 

The  first,  and  oldest,  is  the  Columbian  mottled-gray  clay  of  south- 
eastern and  southwestern  Louisiana.  It  constitutes  the  "pine  flats" 
of  the  coast,  and  the  so-called  "second  bottoms"  of  the  coastal  plain 
These  clays  have  been  worked  at  a  number  of  points,  especially  along 
the  Pearl,  Chefuncte,  and  Sabine  rivers. 

"The  second  group  includes  clays  of  later  Columbian  age,  skirting, 
though  lying  30  to  50  feet  above,  the  alluvial  valley  of  the  modern  Missis- 
sippi River.  Upon  the  eastern  bank  they  form  a  continuous  bluff  from 
the  Mississippi  State  line  to  Baton  Rouge,  thence  bear  southwestward 
to  near  Lake  Mauripas  as  an  escarpment  bordering  the  modern  Mississippi 
alluvium.  Upon  the  immediate  front,  and  extending  some  two  or 
three  miles  back  from  the  river,  these  yellow  and  somewhat  loamy  clays 
are  covered  by  the  brown  loam  or  loess,  and  in  such  position  have  not 
been  worked."  But  at  Baton  Rouge,  where  the  loam  has  been  largely 
removed,  they  are  extensively  dug  for  common  brick. 

Clays  of  similar  character  and  geologic  age  form  a  somewhat  inter- 
rupted escarpment  on  the  western  side  of  the  present  Mississippi  Valley. 
These  clays  have  been  worked  at  Markville,  Washington,  and  New  Iberia, 


332  CLAYS 

and  utilized  for  tile,  common  brick,  and  dry-pressed  brick.  The  heaviest 
and  perhaps  best  of  these  deposits  are  found  in  West  Carroll,  Richland, 
and  Franklin  parishes. 

The  third  group  includes  a  series  of  pocket-like  deposits  in  the  modern 
alluvium  of  the  Red  River. 

Near  Shreveport,  and  further  north  in  the  bluffs  of  Caddo  and  Bossier 
parishes,  are  outcrops  of  lignite  shales  which  may  be  of  value. 

References  on  Louisiana  Clays 

N 

1.  Clendenin,  W.  W.,  Clays  of  Louisiana,  Eng.  and  Min.  Jour.,  LXVI, 
p.  456,  1898. 

2.  Ries,  H.,  Report  on  some  Louisiana  Clay  Samples,  La.  Exp.  Stat., 
Ft.  V,  p.  263,  1899. 


CHAPTER  VI 

MAINE— NORTH  CAROLINA 

Maine,  New  Hampshire,  and  Vermont 

THE  larger  portion  of  these  three  States  is  underlain  by  either  pre- 
Cambrian  crystalline  rocks  or  metamorphosed  Palaeozoic  formations, 
consequently  little  clay  is  to  be  looked  for  in  these.  Covering  the  entire 
surface  of  these  States,  however,  is  a  mantle  of  Pleistocene  deposits, 
mostly  glacial  drift,  which  is  employed  at  many  places  for  the  manufac- 
ture of  bricks,  as  it  often  contains  clayey  members.  None  of  the  deposits 
are  refractory,  and  indeed  they  may  often  be  quite  calcareous.  The 
glacial  clays  are  found  in  the  till  or  have  accumulated  in  hollows,  but 
in  addition  to  these  are  to  be  found  in  a  series  of  estuarine  deposits, 
represented  by  the  clay-beds  that  have  been  formed  in  the  larger  valleys 
during  a  depression  of  the  land  in  Pleistocene  time.  The  subsequent 
uplift  of  the  surface,  and  their  erosion  by  streams,  has  left  the  clays  as 
terrace  deposits  along  the  valleys.  Deposits  of  this  character  are  com- 
monly more  persistent  and  thicker  than  the  preceding  type  of  drift-clay. 
An  extensive  series  underlies  the  terraces  along  the  eastern  shore  of 
Lake  Champlain,  where  they  reach  a  height  of  several  hundred  feet 
above  sea-level.  These  Pleistocene  clays  are  mostly  of  value  only  for 
making  common  brick  and  drain-tile,  although  the  smoother  ones  could 
be  employed  for  red  earthenware. 

A  rather  important  series  of  residual  clays  is  found  in  Vermont  in 
connection  with  limonite  and  manganese  deposits.  They  have  been 
recorded  from  Brandon,  Monkton,  and  Bennington,  as  well  as  in  Shafts- 
bury,  Wallingford,  Plymouth,  and  Chittenden.  Some  of  these  are  of 
white  color,  and  although  now  used  chiefly  for  paper  manufacture,  have 
also  been  tried  for  the  manufacture  of  porcelain,  stoneware,  and  fire- 
brick. The  following  analyses  show  the  composition  of  one  from  Forest- 
dale,  Vt. 

333 


334  CLAYS 

ANALYSES  OF  VERMONT  KAOLINS 

1.  II. 

Silica  (SiO2) 53.70  48  91 

Alumina  (A1,O<) 35. 12  39.99 

Ferric  oxide  (Fe,O.,) 0  06  0  33 

Lime  (CaO),  .  , trace  0.34 

Magnesia  (MgO), trace  

Loss  on  ignition 10 . 55  8 . 92 

Alkalies,  by  difference. 0. 57  1 .  51 


Total 100.00  100.00 

I.  J    N    Nevius   anal. 
II.    H   Carmichael   anal. 

A  decomposed  talcose  schist  known  as  "fire-clay"  is  worked  near 
Rutland,  and  used  for  patent  wall-plaster,  stove-lining,  etc. 

References  on  Vermont  Clays 

1.  Nevius,  J.  N.,  Kaolin  in  Vermont,  Eng,  and  Min.  Jour.,  LXIV. 
p.  189,  1897. 

2.  Perkins,  G.  H.,  Kept.  Vt.  State  Geologist,  1903-1904,  p.  52,  1904. 

Maryland 

The  Maryland  clay-deposits  (Ref .  5)  occur  in  formations  ranging  from 
Algonkian  to  Pleistocene,  and  the  several  formations  of  each  system 
are  each  more  or  less  limited  to  one  of  the  three  topographic  provinces 
into  which  the  State  is  divisible,  as  follows: 

Coastal  Plain  area,  containing  Pleistocene,  Tertiary,  Jura-Trias,  and 
some  of  the  Algonkian  formations;  bounded  approximately  on  north- 
west by  a  line  passing  through  Wilmington,  Baltimore,  and  Washington. 

Piedmont  Plateau  region,  containing  Palaeozoic,  Mesozoic,  and  pre- 
Cambrian  formations.  The  first  two  yield  shales,  while  the  third  gives 
a  series  of  residual  clays  which  may  at  times  be  of  value.  This  region 
extends  from  the  western  boundary  of  the  coastal  plain  to  the  Appala- 
chian Mountains. 

Appalachian  region,  consisting  of  parallel  mountain  ridges  com- 
posed of  upturned  Palaeozoic  strata.  These  are  largely  Devonian  and 
Carboniferous  shales  which  are  abundant  in  Allegany  and  Garret t 
counties. 

Algonkian  Clays 

These  are  exclusively  of  residual  character  and  usually  highly  ferrugi- 
nous; there  are,  however,  in  Cecil  County  a  number  of  scattered  kaolin- 
deposits  derived  from  feldspathic  gneiss,  and  one  near  Northeast  has 


MAINE— NORTH  CAROLINA  335 

been  worked  to  some  extent  for  use  in  paper  manufacture.  A  second 
pit  has  been  worked  near  Dorsey  station  in  Howard  County  and  used 
in  fire-brick  making. 

The  impure,  ferruginous  residuals,  which  have  been  derived  from  a 
variety  of  rocks  and  are  all  red-burning,  vary  in  thickness,  and  except 
in  the  case  of  limestone  residuals  invariably  pass  by  slow  gradation 
into  the  parent  rock  below.  They  are  widely  distributed  in  the  Pied- 
mont area.  A  broad  belt  of  limestone  clay  is  prominent  in  Washington 
County. 

Silurian  Shales 

Most  of  these  occurrences  have  no  value  for  brick  manufacture, 
unless  they  have  at  least  partly  weathered  to  residual  clays.  One  good 
deposit  occurs  near  the  cement-works  at  Pinto,  Allegany  County. 

Devonian  Shales 

• 

These  are  represented  in  Allegany  and  Garrett  counties  by  a  great 
series  of  shales,  sandy  shales  and  shaly  limestones.  In  some  cases  the 
shales  have  been  so  altered  by  folding  that  they  develop  little  or  no 
plasticity  when  ground  and  mixed  with  water,  while  at  other  times  they 
are  of  excellent  value  for  the  manufacture  of  clay-products.  The  most 
important  member  is  the  Jennings  shale,  which  is  well  exposed  east  of 
Cumberland  and  has  been  used  for  the  manufacture  of  a  red  vitrified 
brick. 

Carboniferous  Shales 

These  are  found  in  the  western  part  of  the  State  in  Garrett  County 
and  western  Allegany  County.  The  important  clay-bearing  formations, 
together  with  their  characteristics,  are  as  follows: 

Mauch  Chunk. — A  red  shale  with  interbedded  reddish  sandstones, 
which  at  times  weathers  down  to  a  plastic  clay.  The  outcrops  flank 
the  ridges  of  western  Allegany  and  eastern  Garrett  counties,  but  the 
beds  are  not  worked. 

Pottsville. — This,  the  only  one  of  the  Carboniferous  formations  which 
has  been  commercially  exploited  in  Maryland,  contains  a  valuable  deposit 
of  fire-clay.  The  bed,  which  is  known  as  the  Mount  Savage  fire-clay, 
underlies  the  Mount  Savage  coal,  and  has  already  been  opened  up  at 
several  points  on  Savage  Mountain,  west  of  Frostburg,  Mount  Savage, 
and  Ellerslie  respectively.  Outcrops  have  also  been  found  near  Elaine 
and  at  Swallows  Falls.  The  bed  sometimes  contains  flint-clay  and 
sometimes  plastic  shale,  the  two  occurring  irregularly. 


336  CLAYS 

Allegany. — This  outcrops  on  the  eastern  side  of  the  George's  Creek 
coal-basin  high  up  on  the  western  slope  of  Dans  and  Little  Allegheny 
mountains.  It  contains  many  beds  of  shale,  but  none  are  worked,  and 
it  is  doubtful  if  many  could  be  used  for  clay-product  manufacture. 

Conemaugh. — The  shales  of  this  member  are  usually  argillaceous, 
and  sometimes  associated  with  coal. 

There  are  other  shaly  formations,  but  none  except  those  mentioned 


seem  promising.1 


Cretaceous  and  Jura-Trias  Clays 


The  clay-deposits  of  these  two  ages  underlie  large  areas  in  eastern 
Maryland  and  are  perhaps  the  most  important  clay  series  in  the  State. 
They  are  divisible  into  the  following  groups  in 


Upper  Cretaceous.. 

f  Rancocas 
IMonmouth 
Matawan 

Lower  Cretaceous 

J  Raritan       ] 

|  Patapsco         Potomac. 

Jura  Trias.  .  . 

|  Arundel        j  Group. 

1  Patuxent 

The  Upper  Cretaceous  deposits  of  Maryland  are  a  continuation  of 
similar  beds  in  Delaware  and  New  Jersey  and  cross  the  State  from  north- 
east to  southwest,  being  especially  developed  in  Cecil,  Kent,  Anne  Arundel, 
and  Prince  George  counties.  In  Maryland,  however,  these  deposits 
carry  but  little  clay.  Those  of  the  Potomac  Group  or  Lower  Cretaceous 
are  of  much  importance,  and  consist  of  a  series  of  sand,  sandy  clays,  and 
gravels  which  have  been  deposited  at  different  periods  and  under  vari- 
ous conditions,  the  result  being  that  the  most  unlike  materials  pass  into 
each  other  horizontally.  The  characters  of  the  several  subdivisions  of 
the  Potomac  together  with  their  uses  are  as  follows: 

Patuxent. — This  is  best  developed  in  the  upper  valleys  of  the  Big 
Patuxent  and  Little  Patuxent  rivers  and  is  sometimes  found  resting  on 
the  crystalline  rocks  of  the  Piedmont  Plateau.  It  is  traceable  as  a 
narrow,  irregular,  and  sometimes  broken  belt  from  Cecil  County  on  the 
northeast  across  Harford,  Baltimore,  Anne  Arundel,  and  Prince  George 
counties  to  the  border  of  the  District  of  Columbia.  The  Patuxent  at 
times  contains  beds  of  refractory  clay,  the  best  occurrences  having  been 

'  For  distribution,  see  Reports  on  Allegany  and  Garrett  counties  issued  by 
Maryland  Geological  Survey. 


MAINE— NORTH   CAROLINA  337 

noted  around  Baltimore  and  near  Sewell  in  Harford  County.  The  clays, 
which  commonly  show  low  tensile  strength  and  low  air-  and  fire-shrink- 
age, have  been  used  with  much  success  for  admixture  with  the  more 
plastic  Arundel  clays  in  the  manufacture  of  terra-cotta. 

Arundel  formation. — Although  highly  developed  in  Anne  Arundel 
County,  the  deposits  of  this  horizon  can  be  traced  as  a  broken  belt  from 
Cecil  County  to  the  District  of  Columbia.  The  deposits  form  a  series  of 
large  and  small  lenses  of  clays  bearing  carbonate  iron  ore  (PL  IV,  Fig.  1) 
which  have  commonly  been  deposited  in  old  depressions  in  the  surface 
of  the  Patuxent  formation.  They  vary  considerably  in  size,  ranging 
from  a  few  feet  up  to  125  feet,  and  are  usually  made  up  of  a  blue,  often 
siliceous  clay  of  good  plasticity  but  not  high  tensile  strength.  Cecil, 
Harford,  Anne  Arundel,  Howard,  Prince  George,  and  Baltimore  counties 
all  contain  many  beds  of  Arundel  clay.  They  are  mostly  red-burning 
and  so  their  chief  use  has  been  for  the  manufacture  of  common  and 
pressed  brick,  but  some  has  been  dug  near  Baltimore  for  making  sewer- 
pipe  and  common  pottery,  in  fact  refractory  clay  is  at  times  found  and 
used  for  terra-cotta. 

Patapsco  formation. — The  type  exposures  of  this  are  on  the  shores  of 
the  Patapsco  River,  although  the  formation  extends  across  the  State. 
The  clays  are  chiefly  bright  colored,  mottled  materials,  which  are  often 
surrounded  by  sand-deposits.  At  the  base  of  the  formation  there  is  often 
a  bed  of  bluish  stoneware  clay,  which  is  worked  in  Cecil  County. 

Raritan  formation. — The  beds  in  this  formation  are  predominatingly 
sandy,  and  alt-hough  at  times  they  contain  lenses  of  clay  they  are  of 
far  less  importance  than  those  in  New  Jersey. 

Tertiary  Clays 

An  important  bed  of  red  clay  of  Tertiary  age  extends  from  the 
South  River  southwestward,  showing  many  outcrops,  especially  along 
the  Western  and  Charles  branches  of  the  Patuxent,  at  Upper  Marlboro 
in  the  Potomac  Valley,  in  Prince  George  County,  etc.  It  is  a  somewhat 
fine-grained  plastic  clay,  at  least  20  feet  thick,  and  burns  to  a  good 
hard  red  body,  but  is  not  worked,  although  it  could  be  used  for  pressed 
brick. 

Pleistocene 

This  overlies  the  earlier  formations  of  the  coastal  plain,  and  in  some 
cases  extends  up  on  the  rocks  of  the  Piedmont  Plateau,  forming  a  mantle 
of  sandy  clay,  loam,  and  gravel  of  varying  thickness.  The  loams,  which 
belong  to  the  Columbia  formation,  are  very  extensive  and  form  an  abun- 


338 


CLAYS 


dant  source  of  brick  material,  being  much  used  for  this  purpose  around 
Baltimore. 

Occasionally  the  Pleistocene  carries  stoneware  clays,  as  along  Chesa- 
peake Bay  south  of  Bodkin  Point. 

The  physical  propeities  and  chemical  composition  of  clays  from 
the  different  formations  are  given  below,  all  of  them  being  taken  from 
Volume  IV  of  the  Maryland  Geological  Survey. 

ANALYSES  OF  MARYLAND  CLAYS 


I 

11. 

111, 

IV 

V. 

VI 

Silica  (SiO2) 

70  25 

56.15 

75  40 

69.40 

59  70 

68  30 

Alumina  (Al2Oa) 

17  71 

33  295 

16  73 

19.70 

27.00 

21   27 

Ferric  oxide  (Fe2O3)  
Lime  (CaO). 

4.10 
0  70 

0.59 
0  17 

1.27 
0.35 

2.00 
0.20 

2.10 
0.60 

1.43 
0  52 

Magnesia  (MgO).  . 

0  40 

0.115 

0.90 

0.60 

0.52 

0  80 

Alkalies  (Na2O,K2O).  
Ignition       

1.76 
4  80 

9.68 

0.50 
5.30 

0.62 

7.85 

1.96 
8.20 

0.20 

7  55 

Total  

99.72 

100.00 

100.45 

100.37 

100.08 

100  07 

VII 

VIII. 

IX. 

X. 

XL 

XII. 

Silica  (SiO2)  

72  50 

55  65 

61  00 

46  10 

58  60 

67  50 

Alumina  (Al2Os)  

17  00 

30  53 

26  36 

38  05 

28  71 

17  20 

Ferric  oxide  (Fe^Os) 

1   50 

0  97 

0  83 

1  05 

3  22 

6  70 

Lime  (CaO)  

0  35 

0.75 

0.21 

0  39 

0  40 

0  45 

Magnesia  (MgO)  

0  60 

0  60 

0.10 

0.60 

0  35 

Alkalies  (Na2O,K2O)  

1.10 

0.20 

trace 

0.63 

1.76 

Ignition   

6.50 

12.30 

11.60 

12.95 

8.90 

5  90 

Total 

99  45 

100  35 

100  04 

99  14 

100  81 

99  51 

LOCALITIES  OF  THE  ABOVE 


No. 

Locality. 

Geological  Age. 

Uses. 

J. 

Bottom    shale,    brick    works,    Cumberland, 
Allegany  County.                  

Devonian 

Paving-brick 

II. 
111. 

Flint-clay,  Mount  Savage,  Allegany  County.  . 
Baldwin's    sand-pit,    Raritan    River,    Anne 
Arundel  County  

Carboniferous 
Raritan 

Fire-brick 
Not  worked 

IV 

Bodkin  Point,  Anne  Arundel  County  

Pleistocene 

V 

Baltimore,  Baltimore  County  

Arundel 

Brick 

VI. 

Link's  pit,  south  of  Baltimore,   Baltimore 
County                

Arundel 

Terra-cotta 

VII 

Carpenter  Point   Cecil  County 

Patapsco 

Stoneware 

VIII 

Northeast   Cecil  County  

Algonkian 

Kaolin 

IX. 

x 

Flint-clay,  Swallows  Falls,  Garrett  County.  . 
Shale  Swallows  Falls  Garrett  County 

Carboniferous 

<  t 

Not  worked 

IX. 
XII. 

Upper  Marlboro,  Prince  George  County  
Residual  limestone  clay,  Williamsport,  Wash- 
ington County 

Eocene 
Pleistocene 

it         ii 
Bricks 

MAINE— NORTH  CAROLINA 


339 


PHYSICAL  TESTS  OF  MARYLAND  CLAYS 


I. 

II. 

III. 

IV, 

V. 

VI. 

Per  cent  water  required  

19 

30 

40   . 

19 

22  5 

23 

Air-shrinkage   per  cent. 

4 

6 

11 

4 

6 

6 

.Fire-shrinkage 

5 

4 

9 

6 

g 

10 

Aver.  tens,  strength,  Ibs.  per  sq.  in.   .  . 
f  incipient  fusion.  .         .    . 

55 
01 

40 

8 

223 
05 

65 
3 

77 
1 

110 
01 

Cone  of  \  vitrification  

4 

27  + 

2 

8  + 

6 

8 

[  viscosity  

7 

7 

10 

12 

Plasticity.  .          

lean 

good 

high 

fair 

good 

hiffh 

VII. 

VIII. 

IX. 

X. 

XI. 

XII. 

Per  cent  water  required 

20 

30 

18 

20 

25 

35 

Air-shrinkage   per  cent 

2 

6 

1  5 

5 

4 

9 

Fire-shrinkage 

4 

4 

12  5 

3  5 

5 

11 

Aver.  tens,  strength,  Ibs.  per  sq.  in.  ... 
f  incipient  fusion.  .         . 

10 

27 

40 

8 

20 
10 

100 
3 

15 

27  + 

132 
05 

Cone  of  \  vitrification   

27  + 

27 

8 

Q 

[  viscosity       

10  + 

10 

Plasticity                             

lean 

fair 

lean 

fair 

lean 

fair 

LOCALITIES  OF  THE  ABOVE 


No. 

Locality, 

Geological  Age. 

Uses. 

I, 
II. 
III. 

Savage  Mountain,  Allegany  County.  .  .  . 
Bodkin  Point,  Anne  Arundel  County.  . 
Two  miles  south  of  Bodkin  Point,  Anne 
Arundel  County             .    . 

Mauch  Chunk 
Pleistocene 

tt 

Not  worked 

i<          « 

tt          tt 

IV. 

One-half  mile  south  of  Harman,  Anne 
Arundel  County  

Raritan 

Dry-pressed  brick 

V. 

Link-pit,     Baltimore,     Anne     Arundel 
County   

Arundel 

Terra-cotta 

VI 

Near  Elkton,  Cecil  County  

Patapsco 

Stoneware 

VII 

Leslie,  Cecil  County  

Residual 

Stove-lining 

VIII. 

Patapsco 

Not  worked 

IX 

Northeast  Cecil  County  .  . 

Residual 

Paper-clay 

x 

Shannon  Hill  Cecil  County  

Patapsco 

Not  worked 

XI 

Dorsey   Howard  County         .    .    . 

Residual 

Fire-brick 

XII. 

Upper  Marlboro,  Prince  George  County  . 

Eocene 

Not  worked 

References  on  Maryland  Clays 

1.  Bibbins,  A.,  Md.  Geol.  Surv.,  Report  on  Cecil  County. 

2.  Cook,  R.  A.,  The  Manufacture  of  Fire-brick  at  Mount  Savage, 
Maryland,  Amer.  Inst.  Min.  Eng.,  Trans.,  XIV,  p.  698,  1886. 

3.  Martin,  G.  C.,  Md.  Geol.  Surv.,  Rept.  on  Garrett  County,  p.  212, 
1902. 

4.  Prosser,  C.  S.,  Palaeozoic  Formations  of  Allegany  County,  Jour. 
Geol.,  IX,  No.  5,  p.  409,  1901. 


340  CLAYS 

5.  Ries,  H.;  Report  on  the  Clays  of  Maryland,  Vol.  IV,  Md.  GeoL 
Surv.,  Pt.  Ill,  pp.  205-505,  1902. 

6.  Ries,  H.,  Md.  Geol.  Surv.,  Rept.  on  Allegany  County,  p.  180,  1900. 


Massachusetts 

Most  of  the  clays  dug  in  the  State  are  obtained  from  the  Pleistocene 
formations,  while  comparatively  small  amounts  are  taken  from  the 
Cretaceous  and  Tertiary  strata,  and  residual  clays  are  rare. 

Residual  Clays 

Two  deposits  of  white  residual  clay  or  kaolin  have  been  recorded 
from  Massachusetts.  One  of  these  is  at  Blandford,  Hampden  County; 
the  other  is  4  miles  south  of  Clayton,  Berkshire  County.  The  first 
has  originated  by  the  decomposition  of  a  pegmatite  vein  in  mica-schist, 
and  has  a  width  of  nearly  100  feet.1  It  has  been  used  for  the  manu- 
facture of  white  brick  and  terra-cotta.  The  second  has  been  derived 
from  feldspathic  quartzite  or  gneiss,  and  in  its  crude  state  is  lean 
and  sandy.  The  following  analyses  represent  the  composition  of  washed 
samples  of  the  Blandford  (I)  and  Clayton  (II)  materials. 

ANALYSES  OF  MASSACHUSETTS  KAOLINS 

I.  II. 

Silica  (SiO2) 52.03  50.00 

Alumina  (A12O3) 31 .76  44.00 

Ferric  oxide  (Fe2O3) trace  

Ferrous  oxide  (FeO) 1 .00 

Lime  (CaO) : trace  .024 

Magnesia  (MgO) 54  

Alkalies  (Na2O,K2O) trace  1 . 24 

Water  (H2O) 15.55  


Total 99.88  96.264 

Residual  clays  are  known  in  Essex  County,  but  are  of  no  com- 
mercial value.  One  bed  of  fine  white  kaolin  derived  from  felsite 
occurs  on  the  west  side  of  Kent's  Island,  Newbury.  Another  mass 
is  found  in  South  Lawrence,  but  neither  have  been  worked,  as  they 
are  too  small. 

Crosby,  Technol.  Quart.,  Ill,  1890. 


MAINE— NORTH  CAROLINA  341 


Cretaceous  and  Tertiary  Clays 

The  Cretaceous  and  Tertiary  beds  form  a  thick  series  of  clays  and 
sands,  well  exposed  in  the  Gay  Head  clifts.  The  clay-deposits  are 
pockety,  owing  partly  to  the  frequent  changes  of  conditions  during 
deposition,  and  partly  to  their  subsequent  disturbance  by  the  ice  of  the 
continental  glacier  as  it  advanced  southward.  These  clays  have  been 
used  to  a  slight  extent  for  bricks,  and  somewhat  for  souvenir  pottery. 

Pleistocene  Clays 

These  form  the  most  important  clay  resource  of  the  State,  but  con- 
tain no  high-grade  materials.  They  are  extensively  developed  on  the 
islands  of  Martha's  Vineyard,  Nan  tucket,  and  in  southeastern  Massa- 
chusetts on  Cape  Cod,  but  most  of  these  are  not  well  adapted  to  brick 
manufacture,  as  they  vary  too  much  in  burning. 

The  true  glacial  clays  are  found  and  worked  at  many  points.  (Ref .  6.) 
Some  of  these  were  formed  in  estuaries,  others  in  pools  under  or  in 
front  of  the  ice,  while  still  others  occur  in  the  morainal  drift  and 
represent  ground-up  rock-flour.  In  the  region  south  and  east  of  a 
line  from  the  mouth  of  the  Merrimac  River  to  Stonington,  Conn.,  they 
are  not  found  above  an  elevation  of  100  feet.  Around  Boston  these 
glacial  clays  are  well  developed  in  the  estuaries  of  the  Charles,  Mystic,  and 
Saugus  rivers  north  and  west  of  Boston.  The  clays  are  bluish,  plastic, 
and  very  fine,  but  may  at  times  contain  bowlders  or  scattered  pebbles. 

Similar  clays  are  extensively  worked  along  the  Mystic  River  at 
Medford;  at  Cambridge  and  Belmont  on  the  Charles  River;  at  Holyoke 
and  South  Hadley  on  the  Connecticut;  and  at  Taunton  on  the  Taunton 
River.  They  are  used  chiefly  for  common-brick  manufacture.  There 
are  but  few  published  analyses  of  Massachusetts  clays.  Of  the  two  given 
below,  No.  I  is  a  glacial  clay  from  West  Cambridge,  J.  Card,  analyst, 

ANALYSES  OF  MASSACHUSETTS  CLAYS 

I.  II. 

Silica  (SiO2) 48.99  57.50 

Alumina  (A18O.) 28.90  31.21 

Ferric  oxide  (Fe2O3) 3 . 89  

Lime  (CaO) 7.1  0.19 

Magnesia  (MgO) 3.66  0.20 

Alkalies  (Na2O,K2O) 4.73  0.40 

Water  (H2O) 3.31  9.83 

Total  .,  .100.58  99.33 


342  CLAYS 

and  No.  II  a  red  clay  from  south  end  of  Gay  Head  section.  (7th  Ann, 
Kept.,  U.  S.  Geol.  Surv.,  p.  359.) 

In  Essex  County,  in  which  brickmaking  began  over  200  years 
ago,  Pleistocene  surface-clays  are  much  used  for  bricks  and  pottery. 
They  are  of  variable  thickness,  some  exceeding  thirty  feet  in  depth,  and 
are  worked  at  Danversport,  Haverhill,  Beverly,  and  Salem.  Some  of 
the  deposits  are  excavated  below  sea-level. 

It  is  interesting  to  note  the  variety  of  products  made  from  these  com- 
mon surface-clays,  for  they  include  common  and  pressed  brick,  fire- 
proofing,  and  earthenware.  A  fine  pottery  is  made  at  New  bury  port 
from  a  mixture  of  local  clay  and  Ohio  clays. 


References  on  Massachusetts  Clays 

1.  Brown,  R.  M.,  Clays  of  the  Boston  Basin,   Amer.  Jour.  Sci.,  IV, 
XIV,  p.  445,  1902. 

2.  Crosby,  W.  O.,  Kaolin  at  Blandford,  Mass.,  Technol.  Quart.,  Ill, 
1890. 

3.  Sears,  J.  H.,  The  Physical  Geography,  Geology,  Mineralogy,  and 
Palaeontology  of  Essex  County,  Mass.,  Clays,  p.  357,  1905. 

5.  Shaler,  N.  S.,  Report  on  the  Geology  of  Martha's  Vineyard,  U.  S. 
Geol.  Surv.,  7th  Ann.  Rept.,  p.  297,  1888. 

5.  Shaler,  N.  S.,  Wood  worth,  J.  B.,  and  Marbut,  C.  F.,  The  Glacial 
Brick-clays  of   Rhode  Island  and  Southeastern  Massachusetts,   U.  S. 
Geol.  Surv.,  17th  Ann.  Rept.,  Pt.  I,  p.  957,  1896. 

6.  Whittle,  C.  L.,  The  Clays  and  Clay  Industries  of  Massachusetts, 
Eng.  and  Min.  Jour.,  LXVI,  p.  245,  1898. 


Michigan 

The  clays  of  Michigan  are  derived  from  two  types  of  deposits,  namely, 
(1)  Paleozoic  shales  and  (2)  Pleistocene  clays.  The  former  belong  to 
the  Silurian,  Devonian,  and  Carboniferous. 


Silurian 

Hudson  River.  This  formation  carries  a  number  of  beds  of  shale, 
but  most  of  these  are  either  too  gritty  or  too  calcareous  to  be  used  for 
the  manufacture  of  clay-products. 


THF 

UNIVERSITY 

OF 


MAINE—  NORTH  CAROLINA  343 


Devonian 

Hamilton  shales. — These  outcrop  around  Alpena,  but  have  not  been 
used  in  the  manufacture  of  clay-products,  although  their  chemical  com- 
position seems  to  show  that  they  may  be  promising. 

Marshall  series. — The  shales  of  this  formation  are  very  extensive 
and  are  well  developed  around  East  Jordan,  where  the  mellowed  out- 
crops form  a  very  tough  plastic  clay  and  are  used  in  the  manufacture 
of  brick.  They  form  a  promising  clay  resource,  but  one  objection  to 
them  is  the  occasional  high  content  of  soluble  salts. 

Carboniferous 

The  Carboniferous  shales  found  in  Michigan  belong  in  the  coal- 
measures,  and  are  found  interbedded  with  the  coal-seams  and  sandstones. 
Three  types  were  noted,  namely,  (1)  a  light-gray  shale  often  underlying 
the  coal  and  erroneously  called  fire-clay.  (2)  A  black  fine-grained,  brittle 
shale,  and  (3)  a  dark  grayish-black  shale.  The  last  two  usually  overlie 
the  coal-seam.  The  shales  are  found  associated  with  the  coals  in  the 
different  mines  around  Saginaw,  Owosso,  Corunna,  St,  Charles,  Verne, 
Bay  City,  and  Sebewaing.  When  ground  up.  and  mixed  with  water 
most  of  these  shales  give  a  plastic  mass,  but  one  whose  tensile  strength 
is  usually  low.  They  have  been  found  in  several  places  sufficiently 
plastic  to  be  molded  in  a  stiff-mud  brick-machine,  and  used  to  make 
paving-brick  or  sewer-pipe.  They  usually  vitrify  around  cones  3  and  4 
and  become  viscous  anywhere  from  cones  5  to  11.  The  coal  and  the 
shales  form  a  basin  northeast  of  Saginaw,  which  has  a  diameter  of  about 
50  miles.  The  outcrops  are  found  chiefly  around  the  edge  of  the  basin, 
and  in  the  center  the  shales  are  not  only  at  a  considerable  depth  below 
the  surface  but  there  is  usually  a  heavy  covering  of  glacial  drift  or  lake- 
deposits  at  many  points. 

Michigan  shales. — The  rocks  of  this  series  form  a  belt  from  10  to 
20  miles  wide  surrounding  the  coal-measure  rocks  in  the  lower  peninsula. 
They  are  best  exposed  at  Grand  Rapids,  where  they  form  a  bed  from  6  to 
10  feet  thick  overlying  a  gypsum  deposit,  but  additional  exposures 
occur  in  Huron  and  Arenac  counties,  as  well  as  along  the  Cass  River 
in  Tuscola  County.  From  laboratory  tests  it  is  found  that  the  Michigan 
shales  are  usually  more  fusible  than  those  of  the  coal-measures  and  that 
they  burn  to  a  good  red  color,  although  they  may  in  some  cases  contain 
an  abundance  of  soluble  salts.  Samples  of  them  taken  from  the  weathered 


344 


CLAYS 


outcrops  show  considerable  plasticity.     These  shales  have  been  worked 
for  the  manufacture  of  brick  at  Grand  Rapids. 

Coldwater  shales. — The  deposits  of  this  series  are  very  extensive, 
and  have  been  opened  up  in  quarries  at  Bronson,  Union  City,  and  Cold- 
water  and  on  the  northeast  side  of  the  coal-measure  area,  they  are  well 
exposed  near  Forestville  (PI.  XXIX,  Fig.  1)  on  Lake  Huron.  Many 
beds  of  this  shale  series  will  no  doubt  be  found  to  be  well  suited  for 
the  manufacture  of  clay-products,  for  samples  tested  show  that  they 
vitrify  at  about  cone  2  and  become  viscous  at  cone  5. 

Pleistocene 

The  clays  of  this  age  are  divisible  into  three  groups,  namely,  lake- 
deposits,  river-deposits,  and  moraine-deposits.  All  of  these  are  very  cal- 
careous, except  the  river-clays  which  are  less  so,  but  show  a  high  amount 
of  grit.  In  many  cases  the  lake-clays  have  been  leached  in  their  upper 
portions  and,  being  freed  from  lime,  these  beds  nearer  the  surface  tend 
to  burn  red.  The  lake-clays  are  extensively  developed  at  Detroit,  Port 
Huron,  South  Haven,  Marquette,  Saginaw,  and  Escanaba,  and  are  often 
found  as  much  as  50  or  60  feet  above  the  present  lake-level.  These 
Pleistocene  clays  are  usually  fine-grained,  nearly  always  calcareous,  and 
fuse  at  a  low  temperature.  Their  tensile  strength  commonly  ranges 
from  150  to  170  pounds  per  square  inch.  The  morainal  clays  form  irregular 
masses  in  the  terminal  moraine  and  are  worked  at  Ionia  (PL  XXX, 
Fig.  1)  and  Lansing.  Their  physical  properties  are  similar  to  these  of 
the  lake-deposits.  The  river-clays  are  less  extensive.  No  clays  of  a 
refractory  nature  have  thus  far  been  found  in  the  State.  At  Rowley 
in  Ontonagon  County  there  is  found  a  very  fine-grained  calcareous  clay 
which  has  been  used  as  a  slip. 

ANALYSES  OF  MICHIGAN  CLAYS  AND  SHALES 


I. 

II. 

III. 

IV. 

V. 

Silica  (SiO2). 

55  30 

44  30 

56  50 

53  44 

55  95 

Alumina  (A^Os)   .  . 

14  20 

23  72 

19  31 

24  80 

17  43 

Ferric  oxide  (Fe2O3)  
Lime  (CaO)  

3.62 
0  30* 

7.68 
1  11 

5.89 
1  00* 

0.76 
0  25 

7.67 
2  14* 

Magnesia  (MgO)  

2  61t 

1  50 

1  85f 

1   55t 

Potash  (K2O)  

] 

Soda  (Na2O)  

}    2.15 

2.00 

5.98 

2.86 

2  36 

j>20  75 

Water  (H2O)  

\ 

^21.82 

17.64 

9.47 

| 

12.40 

CaCOa 


=  MgC03. 


PLATE    XXIX 


FIG.  1. — Coldwater  (Carboniferous)  shales  at  White  Rock,  near  Forestville,  Mich. 
(After  H.  Ries,  Mich.  Geol.  Surv.,  VIII,  Pt.  I,  p.  44,  1900.) 


FIG.    2. — Carboniferous    shale   used    for    paving-brick.    Flushing,    Mich.      (After 
H.  Ries,  Mich.  Geol.  Surv.,  VIII,  Pt.  I,  p.  29,  1900  ) 

345 


MAINE—  NORTH  CAROLINA 

ANALYSES   OF   MICHIGAN   CLAYS   AND  SHALES  —  Continued 


347 


VI. 

VII. 

VIII. 

IX. 

X. 

Silica  (SiO2).             .    .  . 

61  09 

54  62 

44  15 

41  86 

52  92 

Alumina  (AlgOa)  

19  19 

12  82 

10  00 

10  70 

12  25 

Ferric  oxide  (FeaOa).  ... 

6  78 

2  00 

4  08 

5  02 

6  45 

Lime  (CaO)  

2  51 

13  68 

24  64* 

14  33* 

13  84* 

Magnesia  (MgO)  

0  65 

4  25 

1  50f 

2  81f 

3  55f 

Potash  (K2O)            .    ... 

Soda  (Na2O)                 .    . 

}    3-16j 

J 

1.55 

2.80 

3.35 

Carbon  dioxide  (CO2).  .  « 

12.01 

14  50 

Water  (H2O) 

5  13  J 

12  13 

8  00 

7  14 

Organic  -f* 

SO3  1  .  42 

1  95 

*  =  CaCO3.  t  =  MgCO3. 

PHYSICAL  TESTS  OF  MICHIGAN  CLAYS  AND  SHALES 


I. 

III. 

IV. 

V. 

VIII. 

Per  cent  H2O  required  for  mixing  .  .  . 

20 

32 

21 

18 

Tensile  strength  ...               .        ... 

55-65 

105 

125-139 

80-95 

Plasticity.  .                              

fair 

coed 

good 

hiffh 

Air-shrinkage   per  cent  

4 

6 

7 

7 

g 

Fire-shrinkage   per  cent  

6 

10 

9 

6 

Incipient  fusion   cone.       

1 

05 

03 

05 

05 

Vitrification    cone.  .       

4 

01 

2 

01 

2 

Viscosity,  cone                

9 

3 

5 

2 

3-4 

Color  when  burned  

red 

red 

red 

deep  red 

buff 

LOCALITIES  OF  THE  ABOVE 


No. 

Locality. 

Geological  Age. 

Uses. 

I. 
II. 

Saginaw  
Grand  Ledge.  . 

Coal-measures  
Carboniferous  

Not  worked 
Sewer-pipe 

Ill 

Grand  Rapids 

Michigan  series  .  . 

Common  brick 

IV 

Coldwater.  . 

Coldwater  series  . 

(i          it 

v 

East  Jordan  . 

Devonian 

Brick  Portland  cement 

VI 

Alpena.  .  . 

Hamilton  shale. 

Portland  cement 

VII. 
VIII 

Marquette.  .  .  . 
Ionia.  .  .  . 

Quaternary  (lake).  .  .  . 
'  '           (glacial) 

Not  worked 
Brick 

IX. 
X. 

Lansing  
Rockland  

"                 '* 

(lake).  .'.  .' 

Red  and  white  brick,  white  tile 
Slip-glazing 

All  of  the  above  are  taken  from  Vol.  VIII,  Pt.  I,  of  the  Michigan  Geological  Survey. 

References  on  Michigan  Clays 

1.  Fall,  D.,  Marls  and  Clays  in  Michigan,  Mich.  Miner,  III,  No.  11, 
p.  11,  1901,  and  Mich.  Geol.  Surv.,  VIII,  Pt.  Ill,  p.  343,  1903. 

2.  Ries,  H.,  Clays  and  Shales  of  Michigan,  Mich.  Geol.  Surv.,  VIII, 
Pt.  I,  1900. 


348  CLAYS 

3.  Russell,  I.  C.,  The  Portland  Cement  Industry  of  Michigan,  U.  S. 
Geol.  Surv.,  22d  Ann.  Kept,,  Pt.  Ill,  p.  629,  1902. 

Minnesota 

The  clays  of  this  State  can  be  divided  into  two  groups,  namely,  (1) 
residual  clays  and  (2)  transported  clays. 

Residual  Clays 

These  have  been  derived  from  either  crystalline  rocks  or  limestones. 
Crystalline  rocks  are  abundant  in  certain  parts  of  the  State,  but  what- 
ever clays  may  have  been  formed  from  them  have  been  largely  removed 
by  glacial  erosion.  Deeply  decayed  granitic  gneisses  are,  however,  ex- 
posed at  a  few  places  in  the  Minnesota  Valley,  as,  for  example,  at  Redwood 
Falls,  but  the  deposits  appear  to  be  of  little  value.  Limestone  residuals 
occur  in  the  "driftless  area"  of  southeastern  Minnesota,  but  they  are 
overlain  by  the  loess,  and  the  two  are  worked  together  for  brick  manu- 
facture. 

Transported  Clays 

Pre-Cambrian 

Argillaceous  slates  of  Kewaatin  age  have  been  worked  for  making 
dry-press  brick  at  Thompson,  thirty  miles  southwest  of  Duluth;  but  the 
enterprise  has  not  been  highly  successful,  although  the  plant  was  in 
operation  in  1904. 

Ordovician 

Shales  of  this  age  are  found  only  in  the  southeastern  quarter  of 
the  State,  and  are  well  exposed  in  the  Minnesota  river  bluffs  near  St. 
Paul.  The  shales  are  usually  interstratified  with  limestones,  and  may 
themselves  be  calcareous,  so  that  only  certain  beds  can  be  used.  These, 
however,  have  been  successfully  worked  at  St.  Paul  for  pressed-brick 
manufacture. 

Cretaceous 

The  Cretaceous  beds  are  probably  the  most  valuable  clay  resource 
of  the  State,  but  unfortunately  the  only  important  occurrence  occupies 
but  a  very  limited  area  near  Red  Wing  (PL  XXX,  Fig.  2),  where  it  has 
been  worked  for  some  years  to  make  an  excellent  grade  of  stoneware. 
Other  deposits  are  known  in  the  western  half  of  the  State,  but  are  deeply 
covered  by  drift  as  well  as  being  of  poor  quality. 


PLATE  XXX 


FIG.  1. — Deposit  of  calcareous  glacial  clay,   Ionia,  Mich.     (After  H.  Ries,  Mich. 
Geol.  Surv.,  VIII,  Ft.  I,  p.  52,  1900.) 


FIG.  2. — Cretaceous  stoneware-clay,  Red  Wing,  Minn.     (Photo  loaned  by  Red  Wing 

Stoneware  Co.) 

349 


MAINE— NORTH  CAROLINA 


351 


Pleistocene 

Glacial  clays,  represented  by  t ill-deposits,  lake-deposits,  or  stream- 
deposits,  are  of  importance  in  Minnesota,  for  common-brick  manufacture 
at  least.  They  are  either  red-  or  cream-burning,  depending  on  the  pre- 
dominance of  iron  or  lime. 

Representative  of  the  first  of  these  three  subtypes  are  the  deposits 
near  Princeton,  Mille  Lacs  County.  Those  of  the  second,  which  were 
probably  of  interglacial  age,  occur  near  the  eastern  border  of  the  State, 
a  specially  important  one  being  worked  at  Wrenshall,  Carlton  County. 
The  third  subtype,  which  includes  river  silts  deposited  during  the  with- 
drawal of  the  ice,  is  prominent  in  two  areas,  namely,  along  the  present 
Minnesota  River  from  Shakopee  to  New  Ulm  and  along  the  Mississippi 
River  from  Minneapolis  to  Little  Falls.  In  both  cases  the  worked  clays 
underlie  terraces  bordering  the  present  river  channels.  They  are  exten- 
sively worked  at  Chester  and  Minneapolis. 

.Loess-deposits. — Most  of  the  clays  worked  on  a  small  scale  belong 
to  this  type,  but  all  are  not  true  loess  accumulations.  In  this  class 
belong  the  Red  River  Valley  clays,  worked  at  Moorhead  and  East 
Grand  Forks. 

ANALYSES  OF  MINNESOTA  CLAYS 


I. 

II. 

III. 

IV. 

Silica  (SiOo)  

69  84 

60-31 

59  72 

73  34 

Alumina  (AljOs)  

23  07 

23  77 

30  00 

14  75 

Ferric  oxide  (Fe-iOs) 

0  48 

7  96 

5  45 

Lime  (CaO)  

0.11 

2  5 

0  82 

0  28 

.Magnesia  (MgO).  

0.14 

1.75 

0  51 

0  05 

Potash  (KoO) 

\ 

Soda  (Na2O) 

>    trace 

2.42 

trace 

Water  (H-.O) 

6  35 

10  34 

4  71 

Total  ,  

90.99 

98.71 

101.39 

98.58 

I.   Red  Wing,  Good  hue  County      J    H.   Rich  sewer-pipe  works. 
II.  Minneapolis,  McLeod  County      M.  C.  Madsden,  anal, 

III.  Ottawa,  Lesueur  County      Ottawa  Brick  Co. 

IV.  Mankato,  Blue  Earth  County.     Minn,  Geol.  Surv.,  1872. 

References  on  Minnesota  Clays 

1.  Berkey,  C.  P.,  Origin  and  Distribution  of  Minnesota  Clays,  Amer. 
Geol.,  XXIX,  p.  171,  1902. 

2.  Winchell,  A.,  County  descriptions  in  the  series  of  Final  Reports, 
Vols.   I,   II,   and   IV  of  the  Minn.   Geol.   and   Nat.   Hist.   Surv. 

3.  Winchell,  N.  H.,  Brick  Clays,  Minn.  Geol.  and  Nat.  Hist.  Surv,, 
Miscel.  Pub.,  No.  8,  1881. 


352  CLAYS 

Mississippi 

The  clay -bearing  formations  of  Mississippi  include  the  Devonian, 
Carboniferous,  Cretaceous,  Tertiary,  and  Pleistocene,  but  little  informa- 
tion has  been  published  regarding  them. 

The  clays  of  the  Potomac  formation  of  the  Cretaceous,  and  the 
Lignitic  formation  of  the  Eocene,  are  probably  of  considerable  value. 

The  Potomac  formation,  which  occupies  a  narrow  zone  extending 
from  Tishomingo  County  on  the  north  to  Monroe  County  on  the  south, 
consists  of  gravels,  sands,  clays,  and  some  lignite  beds,  and  is  overlain 
unconformably  by  the  Lafayette  and  Columbia  formations. 

The  clays  are  of  various  colors,  some  being  white,  but  the  percentages 
of  iron  oxide  indicated  by  the  analyses  show  that  they  are  not  white- 
burning.  They  have  been  used  at  Miston,  Itawamba  County,  for  common 
stoneware. 

The  Lignitic  clay  belt  "extends  from  northern  Marshall  County  to 
the  Alabama  line  along  the  eastern  border  of  Lauderdale  County,  but 
the  better  grades  of  clay  occur  along  a  line  passing  through  the  central 
part  of  the  outcrop  of  the  formation. 

The  clay-deposits  are  known  to  occur  at  a  number  of  points,  but 
Holly  Springs,  where  the  materials  are  worked  for  making  common  stone- 
ware, appears  to  be  the  most  important  locality.  Most  of  the  published 
analyses  indicate  too  high  a  contents  of  iron  oxide  to  be  white-burning. 
Not  a  few  are  apparently  fire-clays,  but  few  would  be  classed  as  highly 
refractory  from  the  analyses. 

References  on  Mississippi  Clays 

1.  Eckel,  E.  C.,  Stoneware  Clays  of  Western  Tennessee  and  North- 
western Mississippi,  U.  S.  Geol.  Surv.,  Bull.  213,  p.  382. 

2.  Hilgard,  E.  W.,  Report  on  the  Geology  of  Mississippi,  p.  244,  1844. 

3.  Logan,  W.  N.,  and  Hand,  W.  F.,  Preliminary  Report  on  the  Clays 
of  Mississippi,  Geol.  Surv.  Miss.,  Bull.  3,  1905. 

Missouri 

In  the  variety  of  its  clays  Missouri  (Ref.  6)  stands  well  up  towards 
the  head  of  the  clay-producing  States.  As  can  be  seen  from  a  glance 
at  the  map  (Fig.  54) ,  the  clay-bearing  formations  range  from  Cambrian 
to  Pleistocene,  exclusive  of  Cretaceous,  and  Jura-Trias. 

A  discussion  of  the  clays  by  formations  is  not  perhaps  wholly  satis- 
factory, but  is  better  in  order  to  maintain  uniformity  of  treatment  as 
far  as  possible. 


MAINE— NORTH  CAROLINA 


353 


i 

o 

•-*» 

£ 


a. 


_^  o 

" 


O 


354 


ICLAYS 


Palaeozoic  Limestone  Clays 

These  consist  of  four  kinds,  namely,  kaolins,  flint-clays,  ball-clays, 
and  stoneware-clays. 

Kaolins. — The  Missouri  kaolins  occur  south  of  the  Missouri  River 
(Fig.  55)  and  are  separable  into  three  districts.  These,  together  with 
the  formations  in  which  the  kaolin  occurs,  are: 


FIG.  55. — Map  showing  distribution  of  Missouri  kaolins.     (After  Wheeler, 
Mo.  Geol.  Surv.,  XI,  p.  200,  1896.) 

Southeastern  district  of  Cape  Girardeau,  Bollinger,  and  Howell 
counties,  in  Ordovician  and  Cambrian  limestones. 

Central  district  of  Morgan  and  Cooper  counties,  in  Ordovician  lime- 
stone. 

Southwestern  district  of  Aurora  and  Lawrence  counties,  in  Mississip- 
pian  limestone. 

According  to  Wheeler,  the  kaolins  appear  to  be  the  insoluble  fine 
residual  matter  left  by  the  removal  by  solution  of  heavy  beds  of  limestone. 
Only  those  of  the  southeastern  district  have  been  worked,  and  these  to 
but  a  limited  extent.  The  output  has  been  sold  for  use  in  the  manu- 
facture of  white  ware,  paper,  or  kalsomine,  and  Glen  Allen  is  the  most 
important  locality. 

Flint-clays. — These  are  compact,  dense,  flinty  clays  with  a  con- 
choidal  fracture,  which  are  found  filling  pockets  or  basins  in  limestone. 
The  deposits  range  from  50  to  200  feet  in  diameter  and  15  to  50  feet 
in  depth,  while  between  the  limestone  wall  and  the  clay  there  is  usually 
a  sheet  of  sandstone  several  feet  thick  (Fig.  56).  The  pockets  are 
thought  by  Wheeler  to  be  old  sink-holes  in  limestones  that  have  be- 
come filled  by  aluminous  matter  being  washed  into  them,  but  he  further 


MAINE— NORTH  CAROLINA 


355 


suggests  that  since  this  they  have  been  slightly  altered  chemically  by 
leaching  with  a  recrystallization  of  the  kaolinite;  indeed,  their  remark- 
able freedom  from  impurities  and  high  alumina  content  are  puzzling 
features. 

The  flint-clays  occur   in   the  eastern-central   portion   of  the   State 
(Fig.  54),  at  a  distance  of  40  to  140  miles  west  of  St.  Louis,  along  the 


FIG.  56. — Section  of  a  Missouri  flint-clay  deposit.     (After  Wheeler,  Mo.  Geol.  Surv., 

XI,  p,  202,  1896.) 

Wabash,  Rock  Island,  Missouri  Pacific,  and  Frisco  railroads;  but  although 
the  clays  occur  in  sub-Carboniferous  and  Ordovician  limestones,  they 
were  possibly  formed  in  Cretaceous  times. 

The  flint-clays  show  the  following  properties:  hardness,  2.5  to  3.5; 
specific  gravity,  2.33  to  2.45;  slaking  qualities,  none;  plasticity,  very 
low;  tensile  strength,  10  to  38  Ibs.  per  sq.  in.;  air-shrinkage,  2.5 
to  3.5  per  cent;  fire-shrinkage,  9  to  14  per  cent;  incipient  fusion, 
about  2300°  F.,  but  unaffected  at  2700°  F.  and  able  to  withstand 
3000°  F.  Average  composition:  Si(>2,  45.8  per  cent;  Al2O3,40  per  cent; 
H20, 14.2  per  cent.  Their  silica-alumina  ratio  has  led  Wheeler  to  suggest 
that  they  contain  pholerite  rather  than  kaolinite,  or  at  least  a  mixture 
of  the  two.  Flint-clay  bricks  have  high  powers  of  heat  resistance,  but 
low  abrasive  resistance.  They  work  well  in  the  arch  of  an  open-hearth 
furnace  or  in  the  checkerwork  of  a  regenerator. 

Ball-clays. — These  appear  to  have  been  derived  by  the  weathering 
of  flint-clays. 

Stoneware-clays. — These  have  a  similar  origin  to  the  flint-clays, 
but  are  less  pure  and  have  not  been  consolidated  by  secondary  chemical 
changes.  They  are  of  local  extent,  and  are  found  in  rocks  ranging  from 
the  Lower  Carboniferous  down  to  the  Cambrian,  but  the  Burlington 
and  Trenton  limestones  appear  to  be  the  most  favorable  situations. 


356  CLAYS 

Coal-measures 

The  Coal-measures  of  Missouri  contain  two  important  series  of  deposits, 
namely,  plastic  fire-clays  and  impure  shales. 

Plastic  fire-clays. — All  of  the  Missouri  plastic  fire-clays  occur  in 
the  Carboniferous,  at  the  base  of  the  Coal-measures,  and  are  found 
in  the  eastern  part  of  the  State  in  two  different  basins  known  respect- 
ively as  the  St.  Louis  and  Mexico  areas.  The  former  is  on  the  western 
edge  of  the  eastern  interior  coal-field,  and  the  latter  on  the  eastern  edge 
of  the  western  interior  field. 

In  the  St.  Louis  basin  there  are  several  beds  of  clay  and  shale,  but 
only  the  St.  Louis  fire-clay  seam  is  refractory.  This  has  an  average 
thickness  of  6  to  8  feet,  with  a  sandstone  floor,  a  thin  bituminous  coal- 
roof,  and  is  worked  by  shafts  (PI.  XXXI,  Fig.  1)  or  adits.  It  is  hard 
when  fresh,  but  disintegrates  on  exposure. 

A  special  grade  known  as  pot-clay  comes  from  a  purer  and  more 
uniform  seam  near  the  middle  or  top  of  the  bed. 

The  St.  Louis  clay  is  coarse-grained,  often  carries  pyrite,  and  although 
high  in  iron,  still  the  latter  is  uniformly  distributed  and  finely  divided. 
The  range  of  physical  properties  of  this  clay  is  given  by  Wheeler  as 
follows:  average  tensile  strength,  80  to  150  Ibs.  per  sq.  in.;  air-shiink- 
age,  6  to  9  per  cent;  fire-shrinkage,  4  to  8.5  per  cent;  vitrification  at 
2300°  to  2450°  F.;  viscosity,  2500°  to  2700°  F.  This  clay  is  much  used 
for  glass  pots,  zinc-retorts,  and  gas-retorts.  It  also  makes  a  durable 
fire-brick  if  not  exposed  to  excessive  heat,  as  its  fusion-point  does  not 
exceed  cone  30  or  31. 

The  average  composition  of  seven  clays  was  as  follows: 

AVERAGE  COMPOSITION  OF  ST.  Louis  FIRE-CLAY 

Mi  ne- run.  Washed. 

Combined  silica  (SiO,)-  •  •  • 32  32 

Free  silica  (SiOo) 30  25 

Alumina  (A1,OC<) 24  24 

Ferric  oxide  (Fe,O3) 1.9  1 .85 

Ferrous  exide  (FeO) 1.2  1 .00 

Lime  (CaO) 7  .7 

Magnesia  (MgO).  .  , 3  .2 

Potash  (K,O) 5  .55 

Soda<Na?O) 2  .10 

Sulphur  (S) 3  .18 

Sulphur  trioxide  (SO8) 35  .40 

Water  (H,O) 10.5  10 

Moisture 2.7  3 

Total  fluxes 5.5  4  . 8 

The  Mexico  clay  includes  one  bed  which  is  worked  at  Fulton,  Mexico, 
and  Vandalia.  It  ranges  from  6  to  40  feet  in  thickness,  but  only  the 


PLATE  XXXI 


FIG.  1. — Photo   of  shaft-house   and   crushing-house   at   fire-clay  mine,  St.   Louis. 

(Photo  by  L.  Parker.) 


>  2. — Pit  of  Raritan   (Cretaceous)  clays,  Woodbridge,  N.  J.     (After  H.  Ries, 
N.  J.  Geol.  Surv.,  Fin.  Rept.,  VI,  p.  340,  1904.) 

357 


MAINE— NORTH  CAROLINA  359 

lower  6  to  12  feet  are  worked,  and  this  through  shafts.  The  range  of 
physical  properties  is  given  by  Wheeler  as  follows:  Average  tensile 
strength,  40  to  80  Ibs.  per  square  inch;  air-shrinkage,  4  to  5  per  cent; 
fire-shrinkage,  6  to  7  per  cent;  vitrification,  2400°  to  2500°  F.;  viscosity, 
2600°  to  270U°  F.  The  average  composition  is  also  given  by  Wheeler 
as  follows: 

Silica  (Si02) 52.00 

Alumina  (A12O3) 33.00 

Ferric  oxide  (Fe2O3) 1.5 

Lime  (CaO) 5 

Magnesia  (MgO) ' 7 

Alkalies  (Na2O,  K2O) 12.00 

Total  fluxes 3.4 

Stoneware-clays. — Those  found  in  the  coal-measures  are  the  most 
important  known  in  the  State,  including  many  clay-  and  shale-beds,  the 
most  extensive  of  which  are  found  in  Henry  County.  They  have  been 
much  used  by  potteries  in  Kansas  as  well  as  other  portions  of  the  West 
and  Southwest.  The  so-called  fire-clays  of  the  barren  coal-measures 
are  usually  impure,  and  consequently  fusible  and  likely  to  blister  or 
give  a  dark  body  after  burning.  The  true  fire-clays  have  also  been 
used  to  some  extent  for  stoneware. 

Impure  shales. — Many  excellent  beds  of  these  are  found  in  the  coal- 
measures.  They  are  all  impure,  but  are  eminently  useful  for  making 
paving-brick,  sewer-pipe,  drain-tile,  roofing-tile,  terra-cotta,  brick,  and 
hollow  ware,  but  they  are  not  usually  pure  enough  for  refractory  goods,, 
stoneware,  or  white  ware,  and  their  main  use  has  been  for  paving-bricks. 
Nearly  all  of  them  make  a  fair  grade  of  brick  by  any  process  of  molding, 
but  the  majority  have  to  be  finely  ground  or  weathered. 

In  their  physical  properties  the  range  is:  average  tensile  strength, 
50  to  250  Ibs.  per  sq.  in.,  usually  between  125  and  175  Ibs.;  water  re- 
quired for  tempering,  16  to  25  per  cent;  air-shrinkage,  4  to  8  per  cent; 
fire-shrinkage,  1  to  10.6  per  cent,  but  usually  4  to  6  per  cent;  incipient 
fusion,  1500°  to  1700°  F.;  vitrification,  1700°  to  1900°  F. 

The  range  of  chemical  composition  is  given  by  Wheeler  as: 

Silica  (SiO2) 50-75 

Alumina  (A12O3) 10-27 

Ferric  oxide  (Fe2O3) 3-10 

Lime  (CaO) 5-2 

Magnesia  (MgO) 5-2 

Alkalies  (Na2O,  K2O) 3-4 

Water  (H2O) 5-12 

Total  fluxes. .  10-15 


360  CLAYS 

Tertiary 

The  Tertiary  beds  occupy  a  small  area  in  the  southeastern  corner 
of  the  State.  They  contain  much  clay  admirably  adapted  to  stone- 
ware manufacture  and  which  is  dug  to  supply  local  potteries.  An 
important  deposit  is  known  at  Commerce. 

Pleistocene 

Pleistocene  clays  are  widely  scattered  over  the  State,  and  form  the 
main  supply  of  material  for  common  brick,  although  a  few  are  suffi- 
ciently pure  and  plastic  for  stoneware  manufacture. 

Three  types  are  recognizable: 

1.  Loess-clays,  confined  mostly  to  the  neighborhood  of  the  larger 
streams,  especially  the  Missouri  and  Mississippi.     They  are  yellow  to 
brown  in  color,  unstratified,  and  often  of  columnar  structure.     Their 
thickness  is  considerable,  75  to  100  feet  being  common  along  the  lower 
Missouri,  while  at  the  Iowa  line  they  have  a  thickness  of  200  feet.     The 
loess  extends  from  3  to  10  miles  back  from  the  streams,  and  appears 
to  get  stronger  as  the  distance  from  the  rivers  increases,  this  change 
interfering  with  its  being  worked  by  the  mud  process.     It  is,  however, 
the  most  valuable  of  the  surface-clays. 

2.  Glacial  clays,  of  varying  character,  confined  to  the  counties  north 
of  the  Missouri  River  and  rarely  over  50  feet  thick.     The  material  is 
usually  very  strong,  red-burning,  and  often  contains  bowlders  of  con- 
cretions, but  occasionally  shows  beds  of  better  clay  suitable  for  stone- 
ware or  drain-tile. 

3.  Alluvial  clays,  found  along  the  present  streams,  and  of  little  im- 
portance. 

The  tables  on  pp.  361,  362  give  the  analyses  and  phyical  tests  of  a 
number  of  Missouri  clays  which  may  be  regarded  as  representative.1 

References  on  Missouri  Clays 

1.  Keyes,  C.  R.,  The  Geological  Occurrence  of  Clay,  Mo.  Geol.  Surv., 
XI,  "p.  35,  1896.  2.  Keyes,  C.  R,.  Distribution  and  Character  of  Mis- 
souri Clays,  Min.  Indus.,  VI,  p.  127, 1897.  3.  Ladd,  G.  E.,  Notes  on  Cer- 
tain Undescribed  Clay  Occurrences  in  Missouri,  Science,  n.  s.,  Ill,  p. 
691, 1896.  4.  Ladd,  G.  E.,  Mo.  Geol.  Surv.,  Bulls.  Nos.  3  and  5.  5.  Sea- 
man, W.  H.,  Zinciferous  Clays  of  Southwestern  Missouri,  Amer.  Jour. 
ScL,  iii,  XXXIX,  p.  38.  6.  Wheeler,  H.  A.,  Clay-deposits,  Mo.  Geol. 

1  These  were  selected  for  the  writer  by  Professor  H.  A.  Wheeler. 


MAINE— NORTH  CAROLINA 


361 


Surv.,  Xi,  1896.  7.  Wheeler,  H.  A.,  Clays  and  Shales  (Bevier  sheet), 
Mo.  Geol.  Surv.,  IX,  sheet  rept.  No.  2,  p.  57,  1896.  8.  Wheeler,  H.  A., 
Fire-clays  of  Missouri,  Amer.  Inst.  Min.  Eng.,  Bimonthly  Bull.,  Jan.,  1905. 


ANALYSES  OF  MISSOURI  CLAYS 
ULTIMATE  ANALYSES 


I. 

II. 

III. 

IV. 

V. 

VI. 

VIL 

VIII. 

Silica  (SiO2). 

55.12 

72.30 

54.90 

74.39 

43  82 

71  94 

54  80 

72  00- 

Alumina  (Al2Os)  

30.71 

18.94 

18.03 

12.03 

38.24 

17  60 

23  73 

11  97 

Ferric  oxide  (Fe2O3).  ..  . 
Lime  (CaO)  

1.51 
0.54 

0.40 
0.68 

6.03 

2.88 

4.06 
1.50 

0.23 
1.93 

2.35 
0  62 

8.67 
0  64 

3.51 
1  80 

Magnesia  (MgO)  

trace 

0.39 

1.10 

1.52 

0  56 

2  23 

1  35 

Potash  (K2O)  

Soda  (Na2O)  

i  1.37 

0.42 

3.40 

3.01 

0.73 

1.51 

3.80 

3.25 

Moisture  

6.72 

1  01 

Comb  water  

10.56 

7.04 

6.90 

3.17 

14.94 

5  27 

6  00 

6  42 

IX. 

X. 

XI. 

XII. 

XIII. 

XIV. 

XV. 

Silica  (SiO2)  

49.04 

65.01 

61.19 

59.36 

60  70 

73  92 

43  5& 

Alumina  (Al2Oa)        .  .  •  . 

34  85 

19  30 

15  48 

23  26 

18  22 

11  65 

41  48 

Ferric  oxide  (Fe2Oa).  .  .  . 

0  71 

4  91 

5  49 

3  06 

7  58 

4  74 

0  35 

Lime  (CaO) 

1  33 

1  40 

1  95 

0  65 

2  68 

1  45 

0  45 

Magnesia  (MgO)  .  •   ... 

1  04 

0  40 

1  56 

0  42 

trace 

0  60 

Potash  (K2O)  

Soda  (Na2O)  

JO.  85 

2.60 

2.82 

0.63 

3.67 

3.13 

0.20 

Titanic  oxide  (TiO2).  .  .  , 

1  01 

Sulphur  trioxide  (SOa).  . 

0.35 

1.03 

3.11 

2.74 

2  18 

Comb  water  

12.33 

5.51 

9.02 

10.20 

7.77 

3  08 

14  05 

PHYSICAL  TESTS  OF  MISSOURI  CLAYS 


I. 

II. 

III. 

IV. 

V. 

VI. 

VII. 

VIII. 

Size  of  grain  
Aver,    tensile    strength, 
Ibs  per  sq  in. 

C.* 
62 

V.F. 

12 

V.F. 
380 

C. 
131 

V.F. 

8 

V.F. 
150 

V.F. 
115 

F. 
151 

%  H2O  for  plasticity.  .  . 
Plasticity  

14.8 
lean 

23.2 
lean 

22.3 
very 

17.2 
lean 

15.1 
very 

16.5 
plastic 

21.5 
plastic 

18.4 
lean 

Air-shrinkage,  per  cent  . 
Fire-shrinkage,  per  cent. 
Speed 

4.4 
6.4 
R. 

4.0 
8.4 

S. 

plastic 
9.6 
1.4 

S. 

5.7 
4.3 
R. 

i 
lean 

3.1 
11.6 

S. 

5.5 
2.2 

S. 

5.9 

2.8 

V.S. 

5.1 
5.7 
R. 

Incipient  fusion,  degs.  F. 
Complete  fusion.degs.  F. 
Viscosity,  degrees  F.  .  .  . 
Specific  gravity  

2200 
2400 
2600 
2.46 

2200 
2500 

'i!89' 

1600 
1750 
1900 
2.01 

2000 
2000 
2300 
2.09 

2350 
2700 
2700 

2.85 

2100 
2300 
2500 
2.34 

1500 
1700 
1900 
2.37 

2000 
2200 
2200 
2.17 

*C.  =  coarse;  V.F,  =  very  fine;  F.  =  fine;  S.=slow;  R=rapid;  V.S.  =  very  slow. 


362  CLAYS 

PHYSICAL  TESTS  OF  MISSOURI  CLAYS — Continued 


IX. 

X. 

XI. 

XII. 

XIII. 

XIV. 

XV. 

Size  of  grain 

V  F 

c 

V  F 

c 

c 

p 

F 

Aver,    tensile   strength, 
Ibs    per  sq.  in.  . 

198 

92 

273 

78 

177 

173 

13 

%  H2O  for  plasticity  .  .  . 
Plasticity  

23.4 
plastic 

18.4 
slightly 

23.1 
verv 

15.0 
lean 

20 
plastic 

17.1 
plastic 

15.2 

Air  -shrinkage,  per  cent  . 
Fire-shrinkage,  percent. 
Speed  . 

7.7 
9.8 

s 

lean 
5.2 
3.5 
R 

VC1J 

plastic 
8.0 
1.5 
V  S 

6.3 
5.4 
R 

5.3 
8.3 
R 

5.3 
5.5 
R 

2.4 
8.9 

S 

Incipient  fusion,  degs.F. 
Complete  fusion,  degs.  F. 
Viscosity,  degrees  F.  .  .  . 
Specific  gravity.  .  . 

1800 
2100 
2400 
1  69 

1850 
2050 
2250 
2  41 

1650 
1800 
1950 
2  05 

2250 
2450 
2650 
2  41 

1700 
1900 
2100 

1800 
1950 
2050 
1  98 

2400 
2700 
2750 
2  39 

LOCALITIES  OF  THE  PRECEDING 


No. 

Locality. 

Geological  Age. 

Uses. 

I 

Mexico  

Coal-measures 

Fire-brick 

II 

Glen  Allen  

Residual  

White  ware 

III 

Norborne 

Pleistocene    . 

Railway  ballast 

IV 

Jefferson  City 

Coal-measures 

Red  brick 

v 

Leasburg 

Fire-brick 

VI 

Calhoun                                      . 

Coal-measures 

Stoneware 

VII 

Kansas  City  .  .                 

i  i 

Paving-brick 

VIII 

(i         it 

1  1 

Red  brick 

IX 

De  Soto                             

Residual.  .  .  . 

White  ware 

x 

Moberlv  ...                 

Coal-measures 

Paving-brick 

XI 

St  Peter's  

Pleistocene  .  .  . 

Railway  ballast 

XII 

St  Louis  (Evens  and  Howard)  

Coa  1-m  easu  res 

Fire-brick 

XIII 

Prospect  Hill   St   Louis 

(  C 

Roofing-tile 

XIV. 

xv 

St.  Louis  (Hyd.  Pr.  Co.)  
Truesdale  (Kelley's  pit)  . 

f  I 
1  1 

Red  brick 
Fire-brick 

Nebraska 

According  to  E.  H.  Barbour  (Ref.  1),  this  State  contains  an  abun- 
dance of  clays,  the  most  important  being  found  in  the  Carboniferous  and 
Dakota  Cretaceous  formations,  while  others  occur  in  the  Tertiary  and 
Quaternary. 

Carboniferous 

The  rocks  of  this  formation  (Ref.  2)  occupy  a  V-shaped  area  in 
southeastern  Nebraska,  with  the  apex  in  the  vicinity  of  Blair,  and  the 
base  along  the  Kansas-Nebraska  line  from  a  point  near  Wymore  to  the 


MAINE— NORTH  CAROLINA  363 

Missouri  River.  The  Carboniferous,  including  the  Permian,  consists 
of  massive  grayish-yellow  limestones,  interstratified  with  clays,  shales, 
and  an  occasional  layer  of  coal.  "  The  clays  are  usually  of  a  dull-blue 
color  interbedded  with  streaks  of  red  and  buff-colored  sands,  but  there 
are  also  thin  layers  of  disintegrated  limestone,  calcite  concretions,  and 
sand.  ... 

"  Frequently  these  thick  deposits  of  clay  form  prominent  bluffs  along 
either  side  of  the  valley  for  some  distance,  especially  where  the  clay  is 
protected  from  erosion  by  some  overlying  layer  of  a  somewhat  harder 
material,  such  as  limestone.  .  .  .  There  are  also  many  other  available 
clay-banks  along  the  Platte  and  Missouri  rivers,  notably  at  Nebraska 
City,  where  extensive  brick-works  are  in  operation,  utilizing  the  clays 
of  the  Carboniferous  for  vitrified  paving-brick.  Terra-cotta  ware  has 
also  been  made  here.  Other  localities  where  the  clays  are  well  exposed, 
and  in  some  cases  worked,  are  Minorsville,  Peru,  and  Table  Rock." 
Nearly  all  of  the  best  deposits  along  the  Missouri  River  in  southeastern 
Nebraska  are  located  along  the  Nebraska  City  branch  of  the  Burlington 
and  Missouri  Railroad, 

Cretaceous 

The  Dakota  formation  rests  stratigraphically  on  top  of  the  Carbonifer- 
ous, with  an  unconformity  between.  The  surface  underlain  by  it  is  on 
the  west  and  northwestern  sides  of  the  Carboniferous  area,  forming 
a  strip  about  30  miles  wide  and  200  miles  long.  It  also  forms 
a  belt  along  the  Missouri  River  north  of  the  Carboniferous  area. 
The  formation  consists  of  a  series  of  shales  and  sandstones,  but  the 
latter,  owing  to  their  higher  resistance  to  erosion,  stand  out  more  promi- 
nently, so  that  the  mellowed  outcrops  of  the  shales  are  less  noticeable. 
These  shales  vary  from  a  sandy  material  of  yellowish-brown  color  to 
highly  plastic  clays,  the  different  beds  showing  a  great  variety  of  colors. 
Lens-shaped  layers  of  sandstone  are,  however,  not  uncommon  in  the 
shale.  These  Dakota  clays  are  available  at  many  localities,  and  are 
said  to  have  given  excellent  results  for  both  pottery  and  brick  manu- 
facture. 

Loess  and  Alluvium 

The  great  bulk  of  brick  made  in  Nebraska  are  manufactured  from 
loess  and  alluvium  (Ref.  3).  The  loess,  or  "bluff-deposit"  as  it  is 
commonly  called,  consists  of  a  light  buff-colored  loam,  of  generally  uni- 
form texture,  but  containing  some  shells.  It  is  found  over  about  half 
the  area  of  the  State. 


364  CLAYS 

The  alluvium  or  valley-wash  is  a  dark-colored  soil  of  very  fine  tex- 
ture, with  interbedded  layers  of  fine  sand  and  gravel,  and  is  being  deported 
at  the  present  time  in  narrow7  strips  along  nearly  all  the  large  streams 
in  the  State. 

References  on  Nebraska  Clays 

1.  Barbour,  Nebr.  Geol.  Surv.,  I,  p.  202,  1903. 

2.  Gould,  C.  N.,  and  Fisher,  C.  A.,  Ann.  Kept.  Neb.  State  Board  of 
Agric.  for  1900,  pp.  185. 

3.  Fisher,  C.'  A.,  Ann.  Kept,  Neb.  State  Board  of  Agric.  for  1900, 
p.  181. 

New  Jersey 

Nearly  all  of  the  larger  geological  formations  in  the  State  contain 
deposits  of  clay,  but  the  important  ones  belong  to  the  following:  Ordo- 
vician,  Triassic,  Lower  Cretaceous,  Upper  Cretaceous,  Miocene  and 
Pliocene  of  Tertiary  and  Pleistocene. 

Cambrian  and  Ordovician 

The  Cambrian  and  Ordovician  rocks  include  beds  of  limestones  and 
shales  writh  some  beds  of  sandstone  and  quart zite,  and  occur  chiefly  in 
Warren  and  Sussex  counties  in  the  great  Kittatinny  Valley,  but  are 
found  also  at  a  few^  other  localities.  Southwest  of  the  terminal  moraine 
(Fig.  57)  the  limestone  yields  a  sticky  yellow  residual  clay  with  flints, 
and  that  worked  near  Beattystown  is  of  this  character.  The  shale, 
also,  where  found  south  of  the  moraine  is  often  deeply  weathered,  and 
at  Port  Murray  is  utilized  for  the  manufacture  of  fireproofing.  There 
it  is  found  to  be  red-burning,  of  low  plasticity,  and  fusing  about  cone  1. 

.    Triassic 

The  Triassic  or  Newark  series  consists  chiefly  of  red  shales  and  sand- 
stones wdth  masses  of  trap-rock,  and  forms  a  belt  extending  across 
the  State  between  the  Highlands  on  the  northwest  and  Cretaceous  on 
the  southeast.  In  places  the  shale  has  disintegrated  to  a  sandy  clay- 
soil,  wrhich  has  been  used  locally  for  common  brick,  but  the  fresh  shale 
has  in  most  cases  been  found  too  sandy  to  make  into  clay-products, 
although  at  one  point,  Kingsland,  the  shales  have  been  used  with  appar- 
ent success.  They  burn  to  a  hard  red  brick,  but  fuse  at  a  low  cone, 
and  are  not  highly  plastic. 


MAINE— NORTH  CAROLINA 


365 


FIG.  57. — Map  of  New  Jersey  showing  distribution  of  important  clay-bearing 
formations.  (Adapted  from  map  by  Kiimmel  and  Knapp,  N.  J.  Geol.  Surv. 
Fin.  Rept.,  VI,  1904.) 


366  CLAYS 


Cretaceous 

The  New  Jersey  Cretaceous  is  divisible  into  three  parts,  which,  begin- 
ning at  the  bottom,  are:  1.  Clay  series  of  Lower  Cretaceous;  2.  Clay- 
marl  series  of  Upper  Cretaceous;  and  3.  Glaucoriitic  marl  series  (see 
Fig.  57).  Of  these  three,  the  first  contains  many  important  clay- 
deposits,  the  second  some  clays  of  economic  value,  but  the  third  is  of 
no  interest  in  the  present  discussion. 

Lower  Cretaceous  clay  series.— This  was  termed  the  Raritan  or 
Plastic  Clay  series  by  Dr.  Cook  (1878)  and  consists  of  a  number  of  beds 
of  clay,  sand,  and  even  gravel.  The  clays  show  great  variety,  ranging 
from  nearly  white  or  steel-blue  fire-clay  of  high  quality  to  black  sandy 
clays  containing  varying  amounts  of  pyrite,  and  useful  only  for  common- 
brick  manufacture.  A  similar  variation  is  found  in  the  sand-beds.  A 
peculiar  feature  of  the  Raritan  series  is  trie  rapid  alternation  of  strata, 
so  that  the  clays  often  change  suddenly,  both  vertically  and  horizontally, 
much  as  shown  in  Fig.  3.  This  fact  often  makes  it  uncertain  whether 
two  pits  sunk  within  a  short  distance  of  each  other  will  yield  the  same 
kinds  of  clay. 

Notwithstanding  these  frequent  changes  in  character  and  the 
impossibility  of  establishing  divisions  in  the  Raritan  series,  which  can 
be  accurately  identified  at  widely  separated  intervals,  it  is  possible, 
nevertheless,  to  recognize  certain  divisions,  whose  general  features  are 
sufficiently  persistent  to  permit  their  being  traced  throughout  the  region 
of  Middlesex  County  in  which  the  beds  have  been  so  extensively  worked. 
In  other  areas  these  subdivisions  do  not  seem  to  hold. 

The  boundary  between  the  upper  part  of  the  Raritan  clays  and  the 
overlying  clay  marls  is  easily  recognized,  the  upper  bed  of  the  former 
being  a  loose  sand  or  sandy  clay,  while  the  lower  bed  of  the  latter  is 
a  glauconitic  clay,  black  when  fresh,  but  rusty  brown  when  weathered, 
and  often  fossiliferous.  Underlying  the  Raritan  beds  is  the  Triassic 
shale. 

The  Raritan  series  occupies  a  broad  belt  (Fig.  57)  extending  from 
Raritan  Bay  across  the  State  to  Trenton  and  Bordentown,  and  a  much 
narrower  strip  along  the  Delaware  River  to  Salem  County.  Over  most 
of  its  outcrop  across  the  State  it  is  covered  by  later  formations: 

In  the  Middlesex  County  area  the  Raritan  is  divisible  into  nine 
members,  which,  beginning  at  the  bottom  together  with  their  characters, 
are  as  follows: 

1.  Raritan  clays.     This  member  carries  both  a  fire-clay  and  potter's 


PLATE  XXXII 


FIG.  1. — Clay-loam  deposit  of  shallow  character,  west  of  Mount  Holly,  N.  J. 
(After  H.  Ries,  N.  J.  Geol.  Surv.,  Fin.  Kept.,  VI,  p.  122,  1904.) 


FIG.  2. — Pleistocene  brick-clay,  Little  Ferry,  X.  J.     (After  H.  Ries,  X.  J.  Geol. 
Surv.,  Fin.  Rept.,  VI,  p.  374,  1904.) 

367 


MAINE— NORTH   CAROLINA  369 

clay.  The  former  is  usually  drab,  but  sometimes  mottled  or  black, 
and  generally  quite  sandy.  It  is  dug  around  Sand  Hills,  and  sparingly 
at  \Voodbridge  and  Mill  Brook.  Its  main  use  is  for  fire-brick,  and  its 
refractoriness  is  usually  about  cone  27.  The  potter's  clay  is  a  white 
or  Mulsh-white  clay  of  variable  color  and  composition.  It  is  worked 
east  of  Martin's  Dock  and  south  of  Metuchen. 

2.  No.  1  fire-sand,  a  bed  of  quartz-sand. 

3.  Wooibridge  clays.      This,   the   most  important   member  of  the 
Raritan  series,  consists  of  an  upper  bed  of  black,  laminated  sandy  clay, 
and  a  lower  bed  of  fire-clay.    The  laminated  clay  is  red-burning,  plastic, 
and  contains  more  or  less  lignite  and  pyrite;    it  is  extensively  worked 
for  the  manufacture  of  fireproofing,  common  brick,  conduits,  etc.,  and 
large  pits  have  been  opened  in  it  around  South  River,  Sayreville,  and 
other  points. 

The  fire-clay  ranges  from  a  fine-grained  clay  of  high  plasticity  and 
high  refractoriness  (cone  35)  to  sandy  clays  of  lower  grade  fusing  at 
cone  27.  It  can  be  stated  in  general  that  the  bed  is  less  refractory  at 
the  southwest  end.  This  clay  is  used  in  the  manufacture  of  fire-brick, 
pressed  brick,  retorts,  stoneware,  and  as  an  ingredient  in  fireproofing 
and  conduits.  A  small  amount  dug  near  Woodbridge  is  sufficiently 
white-burning  and  refractory  for  white-ware  manufacture. 

4.  No.  2  sand.     Included  in  this  sand  formation  are  two  important 
he:  Is  whose  names  are  somewhat  misleading,  namely,  the  feldspar  and 
kaolin  beds.     The  feldspar  is  a  coarse  feldspathic  sand  or  gravel  with 
more  or  less  decomposed  feldspar  and  pellets  of  white  clay,  while  the 
kaolin  is  not  in  any  sense  such,  but  is  a  micaceous  quartz-sand. 

5.  South    Amboy    fire-clay.     This    outcrops    chiefly    south    of    the 
Raritan  River  between  Sayreville  and  South  Amboy,  but  is  also  found 
at  several  points  north  of  it.     It  is  generally  a  white,  light  blue,  or  red- 
mottled  clay,  ranging  from  15  to  30  feet  in  thickness,  and  varying  greatly 
in  its  quality.     Its  refractoriness  is  moderate. 

6.  No.  3  sand. 

7.  Amboy  stoneware-clay.      An   important  bed  of  stoneware-clay, 
best  exposed  southeast  of  South  Amboy.     Like  the  other  members   it 
is  of  variable  character,  but  the  better  grades  are  used  for  stoneware. 

s.  Laminated  sands  of  little  value. 

9.  Cliffwood  lignitic  sands  and  clays.  These  form  a  series  of  beds 
of  massive  black  clay  and  gray-black  laminated  sands  and  clays,  which 
often  carry  lignite  and  pyrite.  They  are  extensively  exposed  in  the 
brick-pits  around  Cliffwood  and  along  Cheesequake  Creek,  and  are  all 
red-burning. 


370  CLAYS 

The  other  Raritan  areas,  around  Trenton,  Burlington,  Bordentown, 
Bridgeboro,  etc.,  afford  clays  of  refractory  character,  but  it  is  not  pos- 
sible to  correlate  the  sections  with  those  of  Middlesex  County.  The 
Raritan  formation  is  by  far  the  most  important  clay-bearing  formation  in 
New  Jersey  containing  as  it  does  such  a  wide  range  of  materials.  Even  a 
hasty  consideration  of  the  uses  to  which  they  are  put  indicates  in  a 
measure  what  a  wide  range  of  materials  must  be  contained  within  the 
limits  at  the  Raritan  strata,  for  among  the  products  made  from  these 
clays  are  common  brick,  fireproofing,  drain-tile,  conduits,  terra-cotta, 
front  brick,  fire-brick,  stoneware,  earthenware,  tubs,  and  sinks,  foundry 
materials,  paper  filling,  etc.  The  physical  tests  and  chemical  analyses 
on  pp.  372  and  374  will  serve  to  give  a  good  idea  of  their  character. 

Clay-marl  series.  —  The  outcrops  of  this  series  extend  from  the 
shores  of  Raritan  Bay  across  the  State  in  a  southwest  direction  to  the 
Delaware  River  north  of  Salem,  forming  a  belt  varying  in  width  from 
2J  to  8  miles.  Its  base  is  marked  by  a  glauconitic  sandy  clay  which 
weathers  to  a  characteristic  cinnamon-brown,  indurated  earth.  The 
top  is  emphasized  by  the  passage  of  a  bed  of  loose  reddish  sand  with 
quartz  grains  of  pea  size  into  a  compact  greenish  marl.  At  many  points 
a  fossil  bed  1  to  4  feet  thick  is  present.  Five  members  are  recognizable 
as  follows: 

1.  Black,  sandy,  often  glauconitic  clay,  weathering  cinnamon-brown. 

2.  Black,  non-glauconitic  clay,  weathering  to  chocolate. 

3.  Varicolored  sands. 

4.  Black  laminated  sand  and  clay,  strongly  glauconitic  to  the  south- 
west. 

5.  Red  quartz-sand.     Top. 

Both  Nos.  1  and  2  are  important  sources  of  brick-  and  sometimes 
tile-clay,  the  former  being  worked  near  Camden,  Keyport,  High ts town, 
etc.,  and  the  latter  near  Matawan,  Kinkora,  Maple  Shade,  Camden,  etc. 
Indeed,  the  two  are  sometimes  worked  in  the  same  or  adjoining  banks. 

Tertiary 

The  Tertiary  clay-deposits  occur  in  scattered  areas  lying  to  the  south- 
east of  the  Lower  Cretaceous  belt.  They  are  beds  of  irregular  form, 
with  a  tendency  towards  basin-shaped  structure.  Owing  to  the  almost 
universal  mantle  of  sand  over  this  region  and  the  flatness  of  the  surface, 
prospecting  for  the  deposits  is  rendered  more  or  less  difficult. 

The  clay-deposits  recognized  in  the  recent  work  of  the  New  Jersey 
Geological  Survey  are  the  Cohansey,  Alloway,  and  Asbury  clays.  The 


MAINE— NORTH  CAROLINA  371 

Cohansey  is  really  a  sand  formation,  but  carries  many  lenses  of  clay 
which  average  8  to  10  feet  in  thickness.  They  occur  in  the  southern 
portion  of  the  State,  in  Ocean  and  Atlantic  counties,  in  southern  Burling- 
ton, Camden,  and  Gloucester  counties,  and  in  Central  Cumberland  coun- 
ties. Deposits  have  been  worked  at  Rosenhayn,  Millville,  May's  Land- 
ing, Woodmansie,  Whitney's,  etc.  The  clays  are  white,  yellow,  choco- 
late, and  black,  and  sometimes  even  lignitic.  Many  are  buff-burning 
and  semi-refractory,  on  which  account  they  are  much  sought  after  for 
the  manufacture  of  buff  bricks  and  terra-cotta. 

The  Alloway  clay,  which  extends  from  near  Swans  Mills,  Gloucester 
County,  to  a  point  2  miles  south  of  Alloway  in  Salem  County,  is  a  light- 
brown  clay,  of  great  toughness  and  high  plasticity.  Where  weathered 
it  contains  many  joints  often  filled  with  iron  crusts,  which  greatly  diminish 
its  value.  The  Alloway  clay  is  a  red-  and  dense-burning  material,  of 
rather  high  air-  and  fire-shrinkage,  but  excellently  adapted  to  the  manu- 
facture of  stiff-mud  brick  and  drain-tile. 

The  Asbury  clay  is  well  exposed  west  of  Asbury  Park,  and  is  usually 
a  dark  sandy  clay  with  laminae  of  sand,  adapted  only  to  common-brick 
manufacture. 

Pleistocene  Clays 

Pleistocene  clays  are  widely  scattered  over  the  State.  To  the  north 
of  the  terminal  moraine  (Fig.  57)  they  consist  of  first,  basin-shaped 
beds  occurring  in  the  valleys;  second,  stony  clays  or  till  found  in  the 
glacial  drift  (PI.  Ill,  Fig.  1);  and,  third,  estuarine  clays,  occurring  in 
great  abundance  in  the  vicinity  of  Hackensack  (PL  XXXII,  Fig.  2). 
They  are  all  impure  materials  adapted  in  most  cases  only  to  the  manu- 
facture of  common  brick  or  drain-tile. 

In  the  region  south  of  the  terminal  moraine  the  most  important 
clays  are  those  of  the  Cape  May  formation.  These  clays  occur  in  a  sand 
and  gravel  formation,  found  underlying  terraces  along  the  rivers  from 
the  coast  inland  to  an  altitude  of  from  40  to  60  feet.  Along  the  Dela- 
ware River  they  are  specially  prominent,  but  other  points  are  Cohansey 
Creek  near  Bridgeton,  the  Maurice  River  south  of  Millville,  etc.  The 
beds  of  clay  are  usually  of  limited  extent  and  grade  into  sand. 

The  Cape  May  clays  are  of  value  chiefly  for  the  manufacture  of  red 
brick  and  drain-tile,  but  occasionally  small  lenses  of  buff-burning  clays 
are  found. 

Up  to  the  present  time  no  fire-clays  have  been  found  in  the  Cape 
May  formation. 


372 


CLAYS 


In  the  following  tables  will  be  found  the  analyses  and  physical  tests 
of  a  number  of  representative  samples  of  New  Jersey  clays: 


ANALYSES  OF  NEW  JERSEY  CLAYS 


I. 

II. 

III. 

IV. 

V. 

VI. 

Sand  } 

r 

1   £0 

Combined  silica  (biOo).  .  .          J 

66.67 

66.66 

•77  .72 

72.37 

66.12J 

42  80 

Alumina  (Al2Os)  

18  27 

14  15 

15  74 

14  40 

22  07 

38  34 

Ferric  oxide  (te2O3)  

3  11 

3  43 

0  49 

3  43 

1  31 

0  86 

Lime  (CaO)  

1  18 

2,15 

trace 

0  75 

0  50 

Magnesia  (MgO) 

1  09 

0  38 

0  81 

0  49 

0  95 

Potash  (K2O).  .          ... 

2  92 

2  32 

trace 

f  0  26 

Soda  (Na2O)   

1  30 

1  38 

trace 

1  1.60 

1.S1 

1  0  18 

Titanium  oxide  (TiO2)  

0  85 

1  20 

Ignition  

4.03 

8  40 

5  62 

6  70 

7.94 

13.50 

Moisture  

1.10 

VII. 

VIII. 

IX. 

X. 

XI. 

XII. 

Sand  

5.20 

1 

[8.10 

> 

Combined  silica  (SiO2)  
Alumina  (A12O3)   . 

40.40 
38  40 

>  64  .  00 
29  08 

\  39  .  8C 
36  34 

\  60.  1£ 
23  23 

51  .  56 
33  13 

68.38 
20  11 

Ferric  oxide  (Fe2Oa).  . 

1  20 

1   12 

1  01 

3  27 

0  78 

1   71 

Lime  (CaO). 

0  22 

1  00 

trace 

Magnesia  (MgO).  . 

0  25 

0  04 

0  67 

trace 

0  73 

Potash  (K2O).         .        .    . 

0  59 

2  64 

0  15 

2  58 

trace 

2  58 

Soda  (Na2O). 

0  80 

trace 

Titanium  oxide  (TiO2).  .  .  . 

* 

* 

* 

1  91 

1  01 

Ignition   .        

12  50 

6  80 

12  90 

8  54 

12  50 

5  .  55 

Moisture  .    . 

1  30 

1   20 

XIII. 

XIV. 

XV. 

XVI. 

XVII. 

Sand  

c 

28  81 

51  80 

48  40  1 

Combined  silica  (SiO2) 

45.76< 

31   12 

9Q  00 

19  44  J 

68.96 

Alumina  (Al2Os) 

39  05 

26  95 

18  9? 

21  83 

17  87 

Ferric  oxide  (Fe2OO.    .  . 

trace 

1  24 

0  88 

1   57 

3  27 

Lime  (CaO)  . 

0  95 

0  98 

0.25 

Magnesia  (MgO).  . 

0  04 

0  07 

0  24 

0.25 

Potash  (K2O).           

trace 

trace 

0  48 

2  ?4 

1  2.10 

Soda  (NaoO)     

trace 

trace 

Titanium  oxide  (TiO2)  

1  90 

Ignition    

14  46 

9  63 

6  70 

5  -90 

6.95 

Moisture  

0  57 

0  50 

0  80 

*  With  A2103 


MAINE— NORTH  CAROLINA 


373 


LOCALITIES  OF  THE  PRECEDING 


No. 

Locality. 

Geological  Age. 

Uses. 

Ref. 

I 

Little  Ferry 

Pleistocene.  .  . 

Bricks.    . 

B  373 

II 

Budd  Bros.    Camden.  .  . 

Clay  Marl  I. 

Bricks.  . 

B  396 

III. 

H    Hylton    Palmyra.  .           .  . 

Raritan  

Fire-bricks 

B  392 

IV. 

A.  E.  Burchem,  Buckshutem. 

Cape  May  

Bricks  .... 

B  415 

V. 

Clayville    Min.    &    Brick    Co., 
Clayville  

Cohansey  

Conduits  

B409 

VI. 

Geo.  Such,  Burt  Creek  

South  Amboy, 

VII. 
VIII. 
IX. 

E.  Roberts,  Florida  Grove  
Grossman  Clay  Co.,  Sand  Hills  . 
R.  N.  and  H.  Valentine,  Sand 
Hills   .  .* 

Raritan 
do. 
Woodbridge.   .  .  . 

Woodbridge 

Ball-clay  
No.  1  fire-clay 
Top-white  clay 

Fire-bricks 

A  198 
A  135 
A  145 

A  154 

X. 
XI. 

Sayre  and  Fisher,  Sayreville.  .  .  . 
No.  1  fire-clay,  Anness  and  Pot- 
ter Woodbridge.  .  .            .    . 

Woodbridge  .... 
1  1 

Common  brick 
Fire-brick.  .  . 

B467 
B  441 

XII. 
XIII. 

W.  H.  Berry,  Woodbridge  
\V.  H.  Cutter,  Woodbridge   .  .  . 

n 
n 

Sewer-pipe.  .  .  . 
Ball-clay.  .  .  . 

A    82 
B443 

XIV. 

W.  B.  Dixon,  Woodbridge  

Raritan  

Fire-clay.  . 

A    79 

XV. 

XVL 

Extra  sandy  clay,  Lough  ridge 
and  Powers,  Woodbridge.  .  .  . 
S.  A.  Meeker,  Woodbridge  

Woodbridge  .  . 

ft 

Fire-clay  
Stoneware-clay 

A  93 
A  99 

XVII 

D  Haines  &  Son  Yorktown 

Alloway 

Brick  and  tile 

B  496 

A,  Report  on  Clays  of  New  Jersey,  1878.         B,  N.  J.  Geol.  Surv.,  Fin.  Rept.,  VI,  1904. 

References  on  New  Jersey  Clays 

1.  Cook,  G.  H.,  Report  on  the  Clay  Deposits  of  Woodbridge,  South 
Amboy,  and  other  Places  in  New  Jersey,  N.  J.  Geol.  Surv.,  1877. 

2.  Hollick,  A.,  Minerals  from  Fire-clay  Beds  at  Green  Ridge,  Staten 
Island,  Amer  Nat.,  XXV,  p.  403,  1891. 

3.  Hunt,  T.  S.,  On  the  Origin  of  Clays  on  the  Atlantic  Seaboard, 
Amer.  Inst.  Min.  Eng.,  Trans.,  VI,  p.  188,  1879. 

4.  Newberry,  J.  S.,  On  the  Raritan  Clays  of  New  Jersey,  Amer.  Assoc. 
Adv.  ScL,  1869. 

5.  Ries,  H.,  Kummel,  H.  B.,  and  Knapp,  G.  N.,  The  Clays  and  Clay 
Industry  of  New  Jersey,  N.  J.  Geol.  Surv.,  Fin.  Rept.,  Vol.  VI.  1904. 

6.  Smock,  J.  C.,  Mining  Clay,  Amer.  Inst.  Min.  Eng.,  Trans.,  Ill, 
p.  211. 

7.  Smock,  J.  C.,  Plastic  Clays  of  New  Jersey,  Amer.  Inst.  Min.  Eng., 
Trans.,  VI,  p.  177. 


374 


CL^YS 


PHYSICAL  TESTS  OF  NEW  JERSEY  CLAYS 


I. 

11. 

III. 

IV.              V. 

Per  cent 
Air-shrin 
Plasticity 

Average 

Cone  05  - 
Cone    1 
Cone    5 

Cone    8 

Cone  of  A 
Color  wh 

water  required 

18.5 
2 
low 
51 
1.6 
16.14 
4.6 
8.82 
7 
3.2G 

red 

21 
2 
fair 
150 
2 
6.56 

1 
red 

20 
5.3 
fair 
65 
1.3 

1.3 
14.52 
2      « 
12.82 
27 
buff 

32 
7 
fair 
52 

3 
19.69 
5  • 
16.75 

27  + 
buff 

33 
3.4 
fair 
33 

6.2 

14.6 
7.14 

4  + 
white 

kage  per  cent.  .  . 

T.  .       .    . 

tensile  strength,  Ibs.  per  sq.  in. 
'  Fire-shrinkage,  per  cent  
Absorption,  per  cent  
Fire-shrinkage,  per  cent  
Absorption,  per  cent  
Fire-shrinkage,  per  cent  
Absorption,  per  cent  
Fire-shrinkage,  per  cent  
Absorption   per  cent 

isoosity 

en  burned 

VI. 

VII. 

VIII. 

IX. 

X. 

Per  cent 
Air-shrin 
Plasticity 
Average 

Cone  05  < 
Cone     1  < 
Cone    5 

Cone    8 

Cone  of  i 
Color  wh 

water  required  

33 
4.4 
fair 

48 

13.6 
7.07 
13.8* 
6.47 
32 
buff 

33 
5 
fair 
41 

7.1 
13.74 
11 
9.10 
34  + 
buff 

30.5 
7g2°0d 

6.6 
10.17 
7 
9.30 

8 

12 
red 

25.5 
6.5 
good 
88 
1.5 
17.93 
3 
13.61 
3.7 
9.98 
6 
10.70 
12? 
red 

20 

6 
good 
U6 
1.3 
16.54 
2.6 
12.68- 
2.3 
10.17 

8 
red 

kage,  per  cent  

' 

;ensile  strength,  Ibs.  per  sq.  in. 
Fire-shrinkage,  per  cent  
[  Absorption,  per  cent  

Fire-  shrinkage  per  cent 

[  Absorption,  per  cent  

'  Fire-  shrinkage,  per  cent  
Absorption,  per  cent  
Fire-shrinkage,  per  cent  
Absorption,  per  cent  
viscosity. 

en  burned 

XI. 

XII. 

XIII. 

XIV. 

XV. 

Per  cent 
Air-shrin 
Plasticity 
Average 

Cone  05 
Cone    1 
Cone    5 

Cone    8  < 

Cone  of  i 
Color  wh 

water  required 

34.9 
10 
high 
286 
3.3 
11.12 
3.3 
9.92 

10 
red 

27 
7.6 
high 
229 
1 
13.42 
2.7 
8.9 

5.7 
1.21 
12+ 
red 

23.4 
8 
high 
293 
.3 
11.65 
3.3 
6.2 
4 
4.36 
5 

buff 

27.2 

lih 

3.3 
12.46 
6 
5.5 

3.51 
red 

22 
6 
good 
108 
4.3 
7.88 
8.6 
.10 

3  + 
red 

kage   per  cent.  .  . 

T                                                                      .      . 

tensile  strength,  Ibs.  per  sq.  in. 
\  Fire-shrinkage,  per  cent.  .  .  . 

[  Absorption   per  cent  .... 

'  Fire-shrinkage,  per  cent  
,  Absorption,  per  cent  
'  Fire-shrinkage,  per  cent  
Absorption!  per  cent  

{Fire-shrinkage   per  cent 

Absorption,  per  cent  
viscosity  .               

en  burned  

*  Cone  10. 


MAINE— NORTH   CAROLINA 
LOCALITIES  OF  THE  PRECEDING 


375 


No. 

Locality. 

Geological  Age- 

Uses. 

Ref. 

i 

Port  Murray.  .  . 

Hudson  River 

Fireproofing 

A 

11 

Kingsland.  .  .  . 

Triassic 

Brick 

£ 

III. 
IV. 

v 

H.  Hylton,  Palmyra  
C.  S.  Edgar,  Bonhamtown  
W.  H.  Cutter,  Woodbridge 

Cretaceous  
Raritan  
VVood  bridge   fire 

Fire-brick  .... 
Saggers  

C 

I> 

VI. 

R.  H.  and  N.  Valentine,  Sand  Hills, 
No.  1  blue  clay. 

clay  beds  
do 

White  ware.  .  . 
Fire-brick 

K 
F* 

VII. 

No.    1   clay,   An  ness  and    Potter, 
Woodbridge.  .  . 

do 

<  t 

Q 

VIII. 
IX. 

X. 

Sayre  and  Fisher,  Sayreville  
Carman  and  Avery,  Cliffwood.  .  .  . 

Budd  Bros.,  Camden  

Woodbridge  black 
laminated  clay  .  . 
Cliffwood     lami- 
nated sands  and 
clays  
Clay  Marl  I 

Common  brick 

«  <           tt 
(  t           t  ( 

H 

I 
j 

XL 
XII 

One  mile  south  of  Collingswood.  .  . 
Yorktown 

Clay  Marl  II.  ... 
Alloway 

Brick  and  tile  . 

it            <  < 

K 
T. 

XIII 

May's  Landing 

Cohansey 

M 

XIV. 
XV 

A.  E.  Burchem,  Buckshutem  
Little  Ferry 

Cape  May  
Pleistocene 

Common  brick 

N 
o 

Ref. 
449;    E, 
394;  K, 

A,    N.  J.  Geol.  Surv.,  Fin.  Kept.,  VI,  p.  5 
do.,  p.  442;    F.,  do.,   p.  447;   G,  do.,  p. 
do.,  p.  397;  L.,  do.,  p.  495;  M.,  do,  p.  37( 

07;    B,  do.,  p.  374;    C 
140;   H,  do.,   p.  467; 
);  N.,  do,  p.  414;  O,  ( 

5,  do.,  p.  392;    D,  c 
I,  do.,  p.  474;   J,  d 
io.,  p.  373. 

o.,  p. 
o.,  p~ 

New   Mexico 

Adobe  brick  are  made  at  many  points  from  the  calcareous  valley 
clays,  and  common  burned  brick  are  also  manufactured  at  different 
points.  The  Cretaceous  shales  at  Las  Vegas  have  yielded  good  results 
with  the  dry-press  brick  process.  Fire-clays  have  been  worked  at 
Socorro  and  were  formerly  made  into  fire-brick. 

New  York 

The  greater  portion  of  New  York  State  is  underlain  by  sedimentary 
rocks  of  Palaeozoic  age,  ranging  from  the  Cambrian  to  the  Carboniferous 
inclusive.  These  consist  in  very  large  part  of  shales,  but  sandstones 
and  limestones  are  at  times  prominent.  The  Cretaceous  and  Tertiary 
formations,  so  abundant  in  States  farther  south,  are  found  in  New  York 
only,  on  Staten  Island,  Long  Island,  and  Fisher's  Island. 

Overlying  all  of  the  above  are  Pleistocene  deposits.  Residual  clays 
are  rare.  The  clay-deposits  of  the  State  may,  therefore,  be  grouped  as 
follows:  Residual  clays,  Palaeozoic  shales,  Cretaceous,  and  Tertiary 
clays,  Pleistocene  clays. 

Residual  Clays 

These  are  of  but  little  importance  in  New  York  State,  and  may 
be  passed  over  with  the  statement  that  some  deposits  of  kaolin  have 


376  CLAYS 

been  found  east  or  southeast  of  Sharon,  but  so  far  as  known  none  have 
ever  proven  of  economic  value. 

Palaeozoic  Shales 

Those  occurring  in  New  York  State  and  including  beds  of  value  to 
the  clay-worker  belong  to  the  Medina,  Salina,  Hamilton,  Portage,  and 
Chemung.  The  Hudson,  Clinton,  and  Niagara  formations  are  of  little 
or  no  value  for  the  manufacture  of  clay-products.  All  of  these  shale 
formations,  with  the  exception  of  the  Hudson,  form  bands  of  variable 
width  extending  across  the  State  in  an  east-west  direction,  and  their 
distribution  can  best  be  seen  by  reference  to  the  geologic  map  of  New 
York,  from  which  it  will  appear  that  the  oldest  formations  outcrop 
towards  the  north,  in  belts  running  parallel  to  Lake  Ontario.  Their 
•characters  are  briefly  as  follows: 

Hudson  River  shale. — This  formation,  although  widely  distributed 
in  the  eastern  part  of  the  State,  is  of  no  economic  value  for  the  manu- 
facture of  clay-products,  since  it  is  deficient  in  plasticity  and  is  very 
.siliceous. 

Niagara  shale. — This  also,  on  account  of  its  calcareous  and  siliceous 
character,  is  of  little  or  no  value. 

Medina  shale. — Along  the  Niagara  River  at  Lewiston,  and  also  along 
the  Genesee  River,  there  are  outcrops  of  this  rock.  It  is  not  utilized 
in  New  York  State,  but  has  given  good  results  for  dry-pressed  brick  in 
Ontario. 

Clinton  shales. — These  are  about  30  feet  thick  in  places,  notably  in 
eastern  Wayne  County,  and  24  feet  thick  at  Rochester  and  Wolcott 
Furnace.  They  have  not  been  used  and  are  probably  often  calcareous. 

Salina  shales. — This  series  forms  a  belt  extending  from  Syracuse 
westward.  The  shale  is  soft,  weathers  easily,  and  possesses  good  plas- 
ticity, but  may  be  quite  calcareous,  and  not  infrequently  carries  lumps 
of  selenite.  It  is  red-burning,  and  used  for  common  and  paving  brick, 
drain-tile,  or  conduits. 

Hamilton  shale. — Though  extending  from  the  Hudson  River  to  Lake 
Erie,  this  formation  shows  considerable  lithologic  variation  ranging 
from  a  sandstone  to  a  clay-shale.  The  latter  phase  is  more  common  in  the 
western  part  of  the  State.  It  is  worked  for  paving-brick  at  Cairo,  Greene 
County,  and  beds  of  good  quality  are  known  at  Windom,  Erie  County. 

Portage  shale. — This  overlies  the  Hamilton  stratigraphically,  and 
hence  outcrops  to  the  south  of  the  Hamilton  belt.  It  consists  of  shales 
and  sandstones,  the  former  being  well  exposed  along  Cashaqua  Creek, 
also  along  Seneca  Lake  and  at  Penn  Yan,  but  becomes  very  gritty  east 


MAINE-NORTH  CAROLINA 


377 


of  this  point.    The  shale  has  been  worked  at  Angola  for  fireproofing, 
at  Jewettville  for  pressed  brick,  and  at  Hornellsville  for  paving-bricks. 


Chemung  shale. — This  somewhat  extensive  shale  formation,  the  most 
southern  in  New  York  State,  has  been  utilized  at  several  points  for 
making  clay-products.  At  Corning  (PL  XXXIII,  Fig.  1)  it  is  quarried 


378  CLAYS 

for  paving-brick,  at  Alfred  Center  for  roofing-tile,  and  at  Elmira  for 
common  brick. 

Cretaceous  and  Tertiary  Clays 

These  include  the  Cretaceous  clays  of  the  Coastal  Plain  region  of 
Long  Island,  Staten  Island,  and  Fisher's  Island,  as  well  as  some  others 
of  possible  Tertiary  age,  but  the  deposits  are  of  exceedingly  variable 
character,  ranging  from  ferruginous  ones  to  others  of  good  refractori- 
ness. They,  moreover,  partake  of  the  character  of  other  Coastal  Plain 
clays  in  being  often  of  highly  siliceous  character  as  well  as  pockety  or 
lens  shaped  in  form.  The  more  important  points  at  which  these  clays 
.are  exposed  are  at  Kreischerville,  Staten  Island;  Little  Neck  near 
Northport,  West  Neck,  Oyster  Bay,  Wyandance,  and  Farmingdale, 
Long  Island.  All  of  these,  except  the  first  two,  are  adapted  only  to  the 
manufacture  of  common  brick.  The  deposits  at  Glencove  and  North- 
port  have  been  worked  for  a  number  of  years,  those  of  the  latter  locality 
having  been  used  for  fire-brick,  stove-linings,  and  stoneware. 

Pleistocene  Clays 

These  can  be  divided  into  four  groups,  namely,  (1)  morainal  clays; 
(2)  lacustrine  clays;  (3)  pond  deposits;  (4)  estuarine  deposits. 

The  morainal  clays  are  usually  too  stony  to  be  of  any  value,  although 
at  Newfield,  Tompkins  County,  one  lens  in  the  moraine  has  been  worked 
for  fifteen  years. 

The  lacustrine  clays  were  laid  down  during  post-Glacial  time,  when 
the  waters  of  Lakes  Erie  and  Ontario  were  dammed  up  to  the  north  by 
the  retreating  continental  glacier,  and  spread  over  the  land  in  the  western 
.and  northwestern  part  of  the  State,  much  clay  being  deposited  during 
this  time.  These  clays  underlie  the  flats  around  Buffalo,  Lancaster, 
Tonawanda,  and  other  places  in  western  New  York,  and  are  used  for 
making  brick  and  drain-tile.  They  often  contain  lime  pebbles. 

The  pond  deposits  are  widely  distributed  throughout  the  State,  being 
found  in  many  of  the  flat-bottomed  valleys.  They  are  prevailingly 
impure,  often  contain  sandy  streaks,  and  are  rarely  deep.  Most  of 
them  burn  red  and  are  worked  for  common  brick  or  tile,  but  hollow 
t>rick  are  also  manufactured. 

The  estuarine  clays  are  confined  to  the  Hudson  River  and  Champlain 
Valleys,  and  were  deposited  during  post-Glacial  times.  They  form  an 
extensive  and  often  thick  deposit,  which  underlies  the  terraces  border- 
ing these  valleys  (PI.  XXXIII,  Fig.  2).  The  section  usually  involves 
.an  upper  sand-bed,  a  yellow  weathered  clay,  and  a  blue  clay.  The  clays 


PLATE  XXXIII 


FIG.  1. — Bank  of  Chemung  shale  used  for  brick,  Corning,  N.  Y.      (After  H.  Ries> 
N.  Y.  State  Mus.,  Bull.  35,  p.  838,  1900.) 


FIG.   2. — Bank  of  Pleistocene   clay   overlain   by   sand,   Roseton,   N.   Y.      (After 
H.  Ries,  N.  Y.  State  Mus.,  Bull.  35,  p.  698,  1900.) 

379 


MAINE— NORTH   CAROLINA 


381 


are  laminated  materials,  plastic,  red-burning,  and  easily  fusible.  Those 
in  the  Hudson  Valley  especially  are  extensively  dug  for  the  manufacture 
of  common  brick,  but  are  probably  useless  for  much  else,  although  certain 
beds  near  Albany  make  an  admirable  slip-clay  which  is  shipped  to  all 
parts  of  the  United  States. 

In  the  following  tables  there  are  given  a  number  of  selected  analyses 
and  physical  tests  of  New  York  clays: 

ANALYSES  OF  NEW  YORK  CLAYS* 


i. 

II. 

III. 

IV. 

V. 

Silica  (SiO2) 

59  50 

52  30 

65  15 

53  20 

68  34 

\liuniiiii  (AloOs) 

20  60 

18  35 

15  29 

23  25 

19  89 

Kerrrc  oxide  (FegOs)   .     . 

8  00 

6  55 

6  16 

10  90 

0  90 

Lime  (CaO) 

0  80 

3  36 

3  50 

1  0 

0  35 

Magnesia  (MsO)             . 

0  35 

4  49 

1  57 

0  62 

trace 

Potash  (K..O) 

1    o     ,•              f 

4  65 

1       e    T-I 

f 

3  55 

Soda  (NaoO) 

[3.60    j 

1  35 

5.71 

2.69  { 

0.84 

Combined  water  (H2O)  
Miscellaneous  

5  .  50  | 

+  organic 
5.30 

]'    C02   I 

i 
\ 

6.39 

MnO2  0.52 
TiO2    0.91 

6.03 

} 

1    3.  04  / 

SO3     0.41 

} 

VI 

VII. 

VIII. 

XI. 

X. 

Silica  (SiO2)  
Alumina  (A12O3)  

47.40 
39.01 

55.00 

51.61 
19.20 

57.36 
16.20 

51.30 
12.21 

Ferric  oxide  (Fe2O^)  

0.15 

1  34  .  54  j 

8.19 

4.55 

3.32 

Lime  (CaO)  
Magnesia  (MgO) 

trace 
trace 

5.33 
3  43 

7.60 
1  25 

5.34 
3  90 

11.63 
4  73 

Potash  (K.O)  

trace 

Soda  (Nfa2O)  

trace 

>    0  .  48 

5.32 

6.98 

4.33 

Combined  water  (H2O)  
Moisture                       •  .  • 

14.10 

1.22 

/  +  C021 
1    7.25) 

Miscellaneous  

..( 

organic 

1      KA 

1 

1  .50 

*  From  N.  Y.  State  Mus,,  Bull.  35. 
PHYSICAL  TESTS  OF  THE  ABOVE 


I. 

III. 

IV. 

VI. 

Per  cent  H2O  to  form  plastic  mass  
Plasticity  .               .    . 

16 
lean 
15 
3 
6 
cone  .04 
1 
4 

21.4 
fair 
92 
4 
10 
06 
01 
4 

20 
moderate 
61 
4 
9 
06 
01 
3 

38 
fair 
11-14 
10 

8.7 

35+ 
35+ 

Average  tensile  strength,  Ibs.  per  sq.  in 
Air-shrinkage   

Incipient  fusion 

Vitrification 

Viscosity           .  « 

382 


CLAYS 


LOCALITIES  OF  THE  PRECEDING 


No. 

Locality. 

Geological  Age 

Uses. 

I 

Lewiston 

Medina 

Not  worked 

II. 
Ill 

IV. 
V. 
VI. 
VII 

Warners  
Angola  
Alfred  Center.  . 
Near  North  pori 
Kreischerville  .  . 
Roseton  

Salina  
Portage  
Chemung  
Cretaceous  

Pleistocene  

Paving,  common,  and  hollow  brick 
Flue-linings 
Roofing-tile 
Stoneware 
Fire-brick 
Common  brick 

VIII 

Croton  Point 

<  «            <  t 

IX. 

Buffalo  

14 

it             tt 

x 

New  field 

"          (drift) 

Common  and  paving  brick 

References  on  New  York  Clays 

1.  Dwight,  W.  B.,  A  Peculiar  Feature  of  the  Clay -beds  on  the  Western 
Bank  of  the  Hudson,  three  miles  north  of  Newburg,  Trans.,  Vassar  Bros. 
Inst.,  Poughkeepsie,  1884-1885. 

>  2.  Jones,  C.  C.,  A  Geologic  and  Economic  Survey  of  the  Clay-deposits 
of  the  Lower  Hudson  River  Valley,  Amer.  Inst.  Min.  Eng.,  Trans., 
XXIX,  p.  40,  1900. 

3.  Martin,  D.  S.,  A  Note  on  the  Colored  Clays  Recently  Exposed  at 
Morrisania,  N.  Y.  Acad.  Sci.,  Trans.,  IX,  p.  46. 

4.  Merrill,  F.  J.  H.,  Origin  of  the  White  and  Variegated  Clays  of  the 
North  Shore  of  Long  Island,  N.  Y.  Acad.  Sci.,  Annals,  XII,  p.  113,  1900. 

5.  Merrill,  F.  J.  H.,  Note  on  Colored  Clays  at  Morrisania,  N.  Y., 
N.  Y.  Acad.  Sci.,  Trans.,  IX.,  p.  45. 

6.  Prosser,  C.  S.,  Distribution  of  Hamilton  and  Chemung  Series  of 
Central  New  York,  N.  Y.  State  Geologist,  15th  Ann.  Kept.,  p.  87,  1899. 

7.  Ries,  H.,  Clays  of  New  York,  their  Properties  and  Uses,  N.  Y. 
State  Museum,  Bull.  35,  1900. 

8.  Ries,  H.,  Physical  Tests  of  Devonian  Shales  of  New  York  State, 
15th  Ann.  Kept.,  N.  Y.  State  Geologist,  Vol.  I,  p.  673,  1897. 

9.  Ries,  H.,  On  the  Occurrence  of  Cretaceous  Clays  at  Northport, 
Long  Island,  School  of  Mines  Quart.,  XV,  p.  354,  1894, 


North  Carolina 

The  clay-deposits  found  in  North  Carolina  are  of  two  types,  namely, 
residual  clays  and  sedimentary  clays,  these  subdivisions  corresponding 
more  or  less  closely  also  to  geological  ones,  that  is  to  say,  the  residual 
clays  are  derived  from  rocks  of  pre-Cambrian  and  Palaeozoic  age,  while 
the  sedimentary  clays  are  of  Mesozoic  age  or  younger. 


PLATE  XXXIV 


FIG.  1. — Kaolin-mine  near  Webster,  N.  C.,  showing  kaolin  mining  by  circular  pits. 
(After  Ries,  N.  C.  Geol.  Survt,  Bull.  13,  p.  56,  1897.) 


FIG.  2. — Bank  of  Carboniferous  shale  near  Akron,  O.      (Photo  loaned  by  Robinson 

Clay-product  Co.) 

3-3 


MAINE— NORTH  CAROLINA  385 

Residual  Clays 

These  may  occur  in  any  portion  of  the  State  west  of  the  coastal  plain 
region.  The  eastern  border  of  this  area  passes  through  Halifax,  Frank- 
lin, Wait,  Chatham,  Moore,  and  Anson.  The  clays  are  usually  impure 
and  gritty,  and  suited  for  little  else  than  the  manufacture  of  common 
brick,  although  in  a  few  instances,  as  at  Pomona  and  Grover,  they 
may  be  of  semi-refractory  character.  A  noteworthy  exception  to  the 
above  occurrences  are  the  deposits  of  kaolin  which  are  found  in  the 
western  part  of  the  State  in  the  Smoky  Mountain  region.  Here  many 
veins  of  pegmatite,  carrying  coarsely  crystalline  quartz,  feldspar,  and 
mica  (generally  muscovite),  with  some  garnet,  have  been  weathered  to 
kaolin  to  a  depth  of  from  60  to  100  feet.  The  veins  vary  in  width  from 
a  few  inches  to  several  hundred  feet  and  may  be  many  hundred  feet 
long.  They  also  branch  or  curve  and  pinch  or  swell.  The  most  im- 
portant of  these  deposits  is  near  Webster,  but  others  have  been  noted 
at  Syiva,  Jackson  County;  Bostick's  Mills,  Richmond  County;  Troy, 
Montgomery  County;  West's  Mills,  Macon  County;  two  miles  west  of 
north  of  Bryson  City,  Swayne  County;  two  miles  south  of  Hall  Station, 
Jackson  County;  and  two  and  a  half  miles  southwest  of  Canton,  Hay  wood 
County.  All  of  these  kaolins  need  washing  before  they  can  be  shipped 
to  the  market,  and  have  been  extensively  used  for  the  manufacture  of 
white  ware. 

Sedimentary  Clays 

Beds  of  these  are  found  widely  distributed  throughout  both  the 
coastal  plain  area  and  the  broader  upland  valleys  of  the  State. 
In  the  former  area  there  are  many  extensive  beds  of  laminated  clay 
which  are  often  well  exposed  in  the  river-banks  traversing  that  region. 
Most  of  the  clay-deposits  found  in  the  Coastal  Plain  area  are  rather  lentic- 
ular in  their  character  and  pass  horizontally  into  beds  of  sand.  Among 
the  best  deposits  of  sedimentary  clays  thus  far  developed  in  the  State 
may  be  mentioned  those  around  Fayetteville,  Goldsboro,  Weldon,  Greens- 
boro, etc.  They  are  nearly  all  red-burning,  and  are  used  for  the  manu- 
facture of  a  brick  or  drain-tile.  In  many  valleys  of  the  uplands  the 
rivers  are  bordered  by  terraces  underlain  by  clays  of  Pleistocene  age, 
such  clays  being  abundant  along  the  Catawba  River  near  Morgantown 
and  Mount  Holly,  on  the  Clark  River  at  Lincolnton,  along  the  French 
Broad  River  at  Asheville,  and  along  the  Yadkin  River  at  Wilkesboro. 
The  depth  of  these  terrace-clays  commonly  ranges  from  5  to  10  feet,  and 
they  are  in  most  instances  covered  by  from  6  inches  to  a  foot  or  more 


386 


CLAYS 


of  sandy  loam.  The  majority  are  adapted  only  to  the  manufacture  of 
common  brick,  but  here  and  there  we  find  beds  of  very  plastic  material; 
sufficiently  free  from  grit  to  be  used  for  the  manufacture  of  common 
stoneware.  The  Triassic  shales  form  a  narrow  belt  in  Grandville, 
Durham,  Chatham,  Moore,  Southeast,  Montgomery,  and  Anson  coun- 
ties, but  their  value  for  making  clay-products  is  said  to  have  been  but 
little  tested.  At  Pomona  a  weathered-shale  outcrop  has  been  used  in 
the  manufacture  of  sewer-pipe. 

ANALYSES  OF  NORTH  CAROLINA  CLAYS 
ULTIMATE  ANALYSES 


I. 

II. 

III. 

IV, 

V. 

Silica  (SiO2^  

53.07 

45.70 

56  81 

50  17 

64  93 

Alumina  (Al2Oa)  

29.54 

40.61 

20  .  62 

28  77 

17  08 

1.27 

1.39 

6  13 

2  88 

5  57 

Lime  (CaO)  

0.15 

0.45 

0  65 

0  05 

0  43 

\Iasrnesia  (MsjO) 

0  14 

0  09 

0  58 

0  " 

0  59 

Potash  (K2O)  

1.28  | 

Soda  (Na2O)  

0.87  / 

2.82 

4.47 

1.04 

3.85 

Combined  water,  ignition.  .  . 

9.93 
1.29 

8.98 
0.35 

8.60 
1.64 

14.03     J 
2.08     I 

6.58 

2.48 

FeO    l.OC 

VI. 

VII. 

VIII. 

IX. 

X. 

.Silica  (SiO2)  

58.17 

59.27 

70.45 

69.58 

53.75 

Alumina  (A^Os)     •     ,  .  .  .  . 

20.10 

22.31 

17  34 

14  03 

24  91 

Ferric  oxide  (Fe2Os).  .  .  .  .  . 

7.43 

6.69 

3  16 

6  41 

7  99 

Lime  (CaO)          

0.60 

0  25 

0  25 

0  40 

0  70 

jVlagnesia  (MffO)  

0.77 

0.13 

0  22 

0  27 

1   12 

Potash  (KoO)            

Soda  (Na26)             

}    2.60 

0.90 

0.70 

1.65 

2.94 

Combined  water,  ignition   .  . 
Moisture              

7.34 
3.23 

9.00 
1.90 

6.63 
0.98 

5.73 
1.68 

7.60 
1  03 

FeO  0.33 

RATIONAL  ANALYSES 


I. 

II. 

III. 

IV. 

V. 

Clay  substance  

61.99 

96.81 

58.85 

73.19 

53.13 

Free  sand     

36.55 

25.40 

40.65 

26.05 

45.90 

VI. 

VII. 

VIII. 

IX. 

X. 

Clay  substance 

48  09 

67  20 

48  26 

45  47 

34  04 

Free  sand 

52  15 

33  25 

51  50 

51  28 

46"00 

Nos.  I-Xfrom  N.  C.  Geol.  Surv..  Bull.  13,  1897. 


MAINE— NORTH  CAROLINA 


387 


PHYSICAL  TESTS  OF  NORTH  CAROLINA  CLAYS 


I. 

II. 

IV. 

V. 

Per  cent  water  for  working  

28 
good 
8 
5 
39 
slow 
fine 
2100 
2300 
2500 

whitish 
2.24 

42 
lean 
6 
4 
20 
slow 
very  fine 
2300 
2500 
2700  + 

white 
2.43 

30 

very  good 

7 
148 
slow 
fine 
1950 
2100 
2250 
/  gray 
\  brown 
2.35 

28 
good 
8.5 
5 
144 
fast 
medium 
1900 
2050 
2200 

red 
2.55 

Plasticity  

Air-shrinkage,  per  cent. 

Fire-shrinkage,  per  cent. 

Average  tensile  strength,  Ibs.  per  sq.  in. 
Rate  of  slaking.  . 

Texture 

Incipient  fusion    degrees  F. 

Vitrification,  degrees  F  

Viscosity  degrees  F  

Sp°cific  gravity.  .  .  . 

VI. 

VII. 

VIII. 

IX. 

X. 

Per  cent  water  for  working.  . 
Plasticity  

28.5 
fair 
9.8 

7 

84 
slow 
fine 
1850 
2050 
2250 
red 
2.45 

28 
lean 
10 
6 

66 
fast 
coarse 
2100 
2400 
2500 
red 
2.46 

26 
lean 
10 
2 

47 
slow 
coarse 
2150 
2350 
2550 
buff 
2.55 

36 
slight 
9.6 
4.5 

60 
fast 
fine 
1950 
2100 
2250 
red 
2.59 

25 

lean 
5 
10 

74 
fast 
fine 
1900 
2100 
2300 
deep  red 
2.63 

Air-shrinkage,  per  cent  
Fire-shrinkage,  per  cent.  .  .  . 
Average  tensile  strength,  Ibs. 
per  sq.  in  

Rate  of  slaking 

Texture 

Incipient  fusion,  degrees  F.  . 
Vitrification,  degrees  F  

Viscosity,  degrees  F 

'Color  when  burned.  .  . 

•Sp3cific  gravity   .... 

LOCALITIES  OP  THE  PRECEDING. 


No. 

Locality. 

Geological  Age. 

Uses. 

•    I 

Grover     

Residual  

\Vhite  pressed  brick 

II. 

Webster  

<  < 

\Vhite  ware 

Ill 

Greensboro  

4  « 

Brick 

IV. 

N.W.  of  Blackburn.  .  . 

Stoneware 

V. 

Fayetteville  (average).  . 

Bricks 

VI. 

Fayetteville  

Not  worked 

VII 

Green  sboro 

Pleistocene.  .  . 

Brick 

VIII 

Pomona 

Brick 

IX 

\Iorgantown 

Columbia.  .  . 

Not  worked 

x 

Wilkesboro 

C  ( 

«           « 

Nos.  I-X  from  N.  C.  Geol.  Surv.,  Bull.  13,  1897. 


388  CLAYS 

References  on  North  Carolina  Clays 

1.  Holmes,  J.  A.,  Notes  on  the  Kaolin  and  Clay-deposits  of  North 
Carolina,  Amer.  Inst.  Min.  Eng.,  Trans.,  XXV,  p.  929,  1896. 

2.  Kerr,  W.  C.,  and  Genth,  F.  A.,  Report  on  Minerals  and  Mineral 
Localities  of  North  Carolina,  1885. 

3.  Pratt,  J.  H.,  The  Mining  Industry  of  North  Carolina,  N.  Ca.  Geol. 
Survey;  separate  bulletins  issued  for  1901,  1902,  1903,  and  1904. 

4.  Ries,  H.,  Clay-deposits  and  Clay  Industry  in  North  Carolina,  N.  Ca. 
Geol.  Surv.,  Bull.  13,  1897. 


CHAPTER  VII 
NORTH  DAKOTA  TO  WYOMING 

North  Dakota 

THE  North  Dakota  clays  (Ref.  1)  are  found  in  the  Cretaceous,  Ter- 
tiary, and  Pleistocene  formations,  the  first  being  probably  the  most 
important. 

Cretaceous 

Most  of  the  divisions  of  this  system  of  rocks  carry  extensive  deposits- 
of  clay,  whose  character  is  briefly  as  follows: 

Benton  and  Niobrara. — These  two  formations,  composed  chiefly  of 
blue  clays  and  shales,  are  closely  associated  and  similar.  They  are  well 
developed  in  the  central  and  northern  parts  of  the  State,  but  rarely 
appear  along  the  eastern  border.  The  clays  of  the  Niobrara  and  ad- 
joining portions  of  the  Benton  often  carry  carbonate  of  lime  and  small 
amounts  of  iron  pyrites,  alum,  gypsum,  and  lignite. 

Pierre. — This  includes  a  great  accumulation  of  clays  and  shales  found 
throughout  a  large  area  in  the  central  portion  of  the  State.  The  beds 
are  uniform  in  character,  of  a  bluish-gray  color,  and  almost  free  from 
sand,  but  at  times  thin  seams  of  gypsum  occur.  The  formation  is 
prominent  in  the  Pembina  and  Turtle  Mountain  region. 

Fox  Hills. — The  Fox  Hills  group  appears  to  carry  few  clays  of  value. 

Laramie  and  Tertiary 

These  two  formations,  which  are  not  differentiated  by  Babcock, 
extend  over  a  large  portion  of  the  State  west  of  the  Missouri  River, 
and  consist  principally  of  clays,  shales,  and  lignites,  with  occasional 
layers  of  sand  and  sandstone.  Some  of  the  clays  appear  to  be  of  re- 
fractory character,  and  a  number  of  beds,  adapted  to  a  variety  of  pur- 
poses, have  been  noted  around  Dickinson,  where  they  have  been  worked 

380 


390 


CLAYS 


to  some  extent.     Red-burning  shales  occur  with  the  coal  at  Minot  and 
in  Mercer  County. 

Pleistocene 

Pleistocene  clays  of  blue  or  yellow  color,  and  often  of  gravelly  or 
stony  character,  are  found  over  a  large  portion  of  the  State.  They  are 
frequently  calcareous,  and  around  Grand  Forks  are  worked  for  cream- 
colored  brick.  Red-burning  brick-clays  occur  along  the  Missouri  River 
near  Bismarck,  and  are  much  used.  Grayson,  Walhalla,  and  Fargo  are 
also  promising  localities. 

The  following  analyses  are  taken  from  Babcock's  report: 

ANALYSES  OF  NORTH  DAKOTA  CLAYS 


I 

II. 

III. 

IV. 

V. 

VI 

VII. 

VIII. 

Silica  (SiO2)  
Alumina  (AljOs).  ... 
Ferric  oxide  (Fe2O3).  . 
Lime  (CaO)  

72.66 
17.33 
1.05 
0.13 

"6'.36 
0.38 

9.35 

60.79 
16.23 
4.49 
0.65 
1.02 
0.19 
0.28 
16.35* 

56.86 
25.03 
6.11 
0.71 
0.76 
0.50 
0.016 
10.014* 

53.72 
17.78 
3.85 
0.81 
0.50 
0.28 
1.72 
21.82 

58.73 
14.98 
5.63 
2.10 
0.74 
0.16 
0.988 
16.67? 

55.77 
12.15 
4.27 
5.92 
1.90 
0.256 
0.992 
18.742* 

71.  2f. 
21.94 
3.67 
0.74 

o.sr 

51.27 
9.33 
3.52 
11.15 
2.31 
0.50 

J2.08 

Magnesia  (MgO)  
Potash  (K2O) 

!Soda  (Na2O). 

Loss  on  ignition  

*  By  difference. 

I.  Grand  Forks,  brick-clay. 

II.  Clay  with  coal.  Mercer  County. 

III.  Clay  over  coal,  Minot. 

IV.  Clay  under  coal,  Minot. 

V.  Alluvial  clay,  Missouri  River,  Bismarck. 

VI  Lehigh  coal-mine,  east  of  Dickinson. 

VII.  Under-clay,  same  locality,  after  ignition. 

VIII.  Brick-clay,  Grand  Forks. 

References  on  North  Dakota  Clays 

1.  Babcock,  E.  J.,  First  Biennial  Report,  N.  Dak.  Geol.  Surv.,  p.  29, 
1901. 

Ohio 

The  geologic  scale  of  Ohio  includes  strata  ranging  from  the  Ordo- 
vician  to  the  Permian,  while  overlying  these  are  beds  of  Quaternary  age. 


Ordovician  and  Silurian  1 

The  rocks  of  these  two  ages  underlie  a  larger  area  in  the  western 
half  of  the  State,  those  of  the  former  age  being  found  chiefly  in  the 

1  Profs.  E.  Orton,  Jr.,  and  C.  S.  Prosser  have  kindly  given    the   author  much 
information  regarding  the  shale  formations  of  the  State. 


NORTH  DAKOTA  TO  WYOMING 


391 


southwestern  part.     They  include  several  shale  formations,  among  them 
the  Eden,  Lorraine,  Richmond,  Saluda,  and  Osgood;   but  most  of  these 


are  highly  calcareous  and  of  little  value  for  the  manufacture  of  clay- 
products.     The  Saluda  has  been  used  for  drain-tile.1 

1  Ohio  Geol.  Surv.,  Vol.  VII,  Pt.  I,  p.  56. 


392  CLAYS 

Devonian 

The  Devonian  rocks  underlie  a  large  area  in  the  northwestern  corner 
of  the  State,  and  also  extend  across  the  west-central  part  from  Lake 
Erie  to  the  Ohio  River. 

The  shale  formations  are  the  Oletangy  and  the  Ohio.  The  former 
is  20  to  35  feet  thick  in  central  Ohio  with  numerous  outcrops  and  shows 
even  greater  thickness  in  the  northern  part  of  the  State.  It  is  actively 
worked  at  Delaware  for  making  drain-tile  and  fireproofing,  but  has  also 
been  used  at  Columbus  for  the  manufacture  of  sewer-pipe  and  common 
brick. 

The  Ohio  shale  is  divisible,  in  the  northern  part  of  the  State  at  least, 
into  three  parts,  known  as  the  Huron,  Chagrin,  and  Cleveland  shales. 
Professor  C.  S.  Prosser  states  that  the  Chagrin  shale  is  gray  to  greenish, 
and  extends  from  the  Black  River  as  surface  outcrops  along  the  shore 
of  Lake  Erie  in  a  belt  several:  miles  broad  to  Pennsylvania,  and  is  re_ 
garded  as  promising  for  the  manufacture  of  clay-products.  Many  red 
pressed  brick  are  made  from  it  at  Cleveland. 

Lower  Carboniferous 

The  Bedford  shale,  which  is  an  important  shale  formation  extend- 
ing clear  across  the  State,  is  in  part  at  least  frequently  of  red  color; 
but  its  greenish  phases  resemble  the  Chagrin  shales  of  similar  color. 
It  is  worked  at  Bedford,  Akron,  Independence,  and  a  number  of  other 
localities  for  pressed-brick  manufacture;  at  Willow  Station  for  paving- 
brick;  and  at  Summit  Station  for  common  and  sewer  brick.  It  promises 
to  become  one  of  the  most  important  shale  formations  of  Ohio. 

The  Logan  shale,  occurring  in  the  lower  part  of  the  Logan  formation, 
is  now  extensively  used  at  a  number  of  points,  including  Newark,  Han- 
over in  central  Ohio,  and  Sciotoville  in  the  Ohio  Valley  region,  but, 
according  to  Professor  E.  Orton,  Jr.,  is  of  non-refractory  character. 

Professor  E.  Orton  states  (Ref.  2)  that  the  Lowrer  Carboniferous  or 
Maxville  limestone  holds  a  valuable  clay-deposit  at  a  few  places  in  south- 
ern Ohio,  while  in  many  places  in  Kentucky  a  hard  flint-clay  comes  into 
the  section.  It  has  been  worked  largely  at  Sciotoville  and  Portsmouth 
for  fire-brick,  and  is  hence  known  at  the  Sciotoville  clay.  It  also  occurs 
.near  Logan,  Hocking  County. 

Coal-measures 

These  underlie  the  eastern  third  of  the  State.  The  lower  members 
are  found  in  the  western  portion  of  the  area,  while  the  upper  members 


NORTH  DAKOTA  TO  WYOMING  393 

immediately  underlie  the  surface  in  the  middle  and  eastern  parts  towards 
the  Pennsylvania  border.  They  include  the  best  clays  in  the  State, 
and  both  shales  and  clays  are  numerous  throughout  the  entire  series. 

Pottsville  series. — The  section  of  the  Pottsville  formation  shows 
the  following  according  to  Orton:1 

Homewood  (Tionesta)  sandstone 

Mount  Savage  (Tionesta)  coal 

Mount  Savage  (Tionesta)  clay  and  shale 

Upper  Mercer  ore 

Upper  Mercer  limestone 

Upper  Mercer  coal 

Upper  Mercer  fire-clay 

Lower  Mercer  iron  ore 

Lower  Mercer  limestone 

Lower  Mercer  fire-clay 

Conoquenessing  (Massillon)  sandstone  (upper) 

Quakertown  coal-beds 

Quakertown  shales 

Conoquenessing  (Massillon)  sandstone  (lower) 

Sharon  shales 

Sharon  coal 

Sharon  clay 

Sharon  sandstone 

The  important  beds  are  the  Mount  Savage  clay  and  shale,  Upper 
Mercer  clay,  Lower  Mercer  clay,  Quakertown  clay  and  shales,  Sharon 
clay  and  shales.2 

Sharon  shales. — These  overlie  the  Sharon  coal  and  vary  in  thickness 
from  1  to  50  feet.  They  are  usually  dark  blue,  sometimes  almost  black, 
with  heavy  iron-ore  nodules  at  certain  levels.  The  shales  proper  have 
become  the  basis  of  one  of  the  largest  sewer-pipe  industries  in  the  United 
States,  at  Akron  and  its  immediate  neighborhood.  The  same  deposit 
is  also  worked  for  roofing-tile,  but  the  shale  is  usually  high  in  iron  oxide. 

Quakertown  clay  and  shale. — These  occupy  a  space  between  the. two 
divisions  of  the  Conoquenessing  sandstones,  when  such  a  separation 
occurs.  They  overlie  and  underlie  the  Quakertown  coal,  although  the 
latter  may  become  extremely  thin  at  times.  The  shales  or  clays  of  this 

1  The  names  in  parenthesis  are  those  given  in  Orton's  report,  Ohio  Geol.  Surv. 
VII,  while  the  names  in  front  of  them  are  the  later  ones. 

2  Orton,  Ohio  Geol.  Surv.,  VII,  Pt.  1,  p.  59. 


394  CLAYS 

age  have  been  worked  in  Summit,  Portage,  and  Stark  counties.  The 
Summit  deposits  have  furnished  stock  for  the  potteries  of  Springfield, 
and  the  Portage  bed  supplies  the  Mogadore  potteries.  The  Massillon 
Fire-brick  Company  has  developed  an  important  deposit  at  this  horizon. 
It  is  a  streak  of  hard  fire-clay  4  to  5  feet  thick  immediately  underlying 
the  Conoquenessing,  and  representing  the  Quakertown  coal.  The  bottom 
of  the  clay  is  30  feet  above  the  Sharon  coal  (Ref.  2). 

Lower  Mercer  clay  and  shale. — Overlying  the  Lower  Mercer  lime- 
stone there  is  often  an  iron  ore,  while  under  it  is  a  coal-seam  of  little 
value.  Underlying  the  coal  there  is  a  shale  or  more  often  clay,  which 
has  been  extensively  worked  in  Stark,  Tuscarawas,  Muskingum,  and 
especially  Hocking  counties.  The  Columbus  Brick  and  Terra-cotta 
Company  at  Union  Furnace  have  used  it,  and  it  has  also  been  worked 
at  Millersburg,  Holmes  County.  The  clay  shows  considerable  varia- 
tion and  is  nowhere  of  high  character.  The  shale  or  clay  immediately 
overlying  the  Lower  Mercer  limestone  is  also  promising. 

Upper  Mercer  clay  and  shale. — The  Upper  Mercer  coal  is  not  of 
economic  importance,  but  the  accompanying  under-clay  is  more  im- 
portant. It  is  a  light-colored  plastic  clay,  of  wide-spread  occurrence 
in  the  State,  and  at  Haydenville,  Hocking  County,  is  extensively  worked 
under  the  name  of  the  Mingo  clay.  It  is  one  of  the  most  valuable  clay- 
deposits  found  within  the  Haydenville  coal-field,  and  runs  from  8  to  10 
feet  thick. 

Mount  Savage  clay. — This,  formerly  named  the  Tionesta,  occurs 
from  a  few  feet  to  20  feet  above  the  last-named  deposits,  and  there  is 
found  at  times  another  valuable  clay-bed.  It  has  been  used  at  Union 
Furnace. 

Allegheny  or  Lower  Coal-measures 

The  most  important  clay-deposits  of  the  Ohio  coal-measures  are 
given  as  follows: 

Upper  Freeport  clay  and  shales 

Lower  Freeport  clay  and  shales 

Middle  Kittanning  clay  and  shales 

Lower  Kittanning  clay 

Ferriferous  limestone  clay 

Putnam  Hill  limestone  clay  and  shales 

Putnam  Hill  limestone  horizon 

Putnam  Hill  or  Brookville  clay. — This  underlies  the  Brookville  coal 
and  is  a  valuable  clay-deposit  in  several  of  the  central  coal-measure 


NORTH  DAKOTA  TO  WYOMING  395 

counties  of  Ohio,  although  of  no  importance  in  parts  of  western  Penn- 
sylvania. It  is  said  to  be  specially  well  developed  and  largely  worked 
in  Muskingum  County,  but  is  also  of  importance  in  the  counties  of 
Coshocton,  Tuscarawas,  and  Stark,  where  it  has  been  much  used.  Prom- 
ising beds  are  also  mentioned  in  Perry,  Hocking,  and  Vinton  counties. 
It  has  been  worked  at  or  near  Zanesville  for  buff-  or  cream-colored  brick, 
encaustic  -tiles,  and  fire-brick,  and  at  Canton  for  the  manufacture  of 
paving-brick.  Other  workings  are  at  Greenford,  Mahoning  County, 
and  New  Lexington,  Perry  County. 

A  red  shale  said  to  be  of  this  same  age  is  also  worked  at  the  last 
locality. 

In  the  Zanesville  area  the  Brookville  clay  is  stated  to  vary  from 
3  to  10  feet  in  thickness  with  an  average  of  6  feet.  It  is  usually  divisible 
into  an  upper  or  plastic  portion  and  a  lower  or  more  siliceous  division. 

A  section  six  miles  above  Zanesville  on  the  west  side  of  the  river  gave: 

Feet. 

Putnam  Hill  limestone — 

Putnam  Hill  limestone  shale 11 

White  clay 4-5 

Dark  clay 2 

Fire-clay 2 

Sandstone  and  sandy  shale 5 

Brown  clay 14 

Ferriferous  or  Vanport  limestone  and  clays. — The  clays  of  this 
formation  are  light-colored,  plastic,  and  of  fair  quality,  with  a  thickness 
ranging  from  2  to  6  feet.  Professor  E.  Orton,  Jr.,  has  informed  the 
author  that  this  yields  a  valuable  stoneware-clay  in  the  district  running 
from  Zanesville  down  to  New  Lexington  on  the  Cincinnati  and  Muskin- 
gum Valley  Railroad.  It  is  also  used  in  southern  Ohio  around  Scranton, 
either  as  a  potter's  clay  or  for  shipment  as  a  second-grade  fire-clay. 

Lower  Kittanning  clay  and  shale. — These  were  pointed  out  by 
Professor  Orton  to  constitute  the  great  clay  horizon  of  the  State,  and 
lie  stratigraphically  between  the  Ferriferous,  limestone  and  Lower 
Kittanning  coal,  often  filling  the  interval  between  them.  In  the  more 
important  occurrences  its  thickness  ranges  between  8  and  30  feet,  and 
sometimes  is  even  continuous  with  the  clays  above  the  Lower  Kittan- 
ning, only  the  coal-seam  being  between,  and  thus  giving  a  combined 
section  of  not  less  than  50  feet.  The  Lower  Kittanning  clay  is  best  seen 
where  it  enters  the  State  from  Pennsylvania,  and  again  where  it  leaves 
the  State  in  its  extension  into  Kentucky.  At  both  of  these  localities 


396 


CLAYS 


in  the  Ohio  Valley,  namely,  in  Columbiana  and  Jefferson  counties  on 
the  one  side  and  in  Lawrence  County  on  the  other,  it  shows  great  quan- 
tities of  clay  of  good  quality.  Other  counties  in  which  it  has  been 


Shales,  sandstone,  and  concealed. 


Shales, 


Shales,  massive,  Morgantown. 


Limestone,  fossiliferous,  Ames. 


Red  shales                               

M' 

Concealed,  with  shales  and  flaggy  sandstone  

Coal 

...•:.;:.•:::::. 

100 

Shale                                        .                

r 

^ 

Shales  drab.                    

{ 

,_ 

Shales  with  coal,  Masontown  

•>' 

Sandstone,  Mahoning,  and  concealed,  under  river  

130 

112 


FIG.  60. — Section  of  Barren  Measures  opposite  Steubenville,  Ohio. 
(After  White,  U.  S.  Geol.  Surv.,  Bull.  65,  p.  77,  1891.) 

developed  are  Tuscarawas,  Stark,  and  Muskingum;  extensive  mining 
has  gone  on  at  Haydenville,  Hocking  County,  and  Canton,  Stark  County. 
The  plastic  clay  from  this  horizon  is  used  by  the  eastern  Ohio  potteries, 
while  a  flint-clay  is  also  found  at  some  points,  as  in  Stark,  Tuscarawas, 
and  Carroll  counties. 


NORTH  DAKOTA  TO  WYOMING 


397 


The  clay  has  been  used  wholly  or  in  part  for  the  manufacture  of 
saggers,  Rockingham,  yellow  and  stone  ware,  sewer-pipe,  paving-brick, 
and  fire-brick. 

Middle  Kittanning  clay. — This  is  said  to  furnish  a  good  fire-clay  at 
Oak  Hill,  Jackson  County,  and  is  there  used  for  fire-brick.  Nodules 
of  iron  are  seen  in  many  of  its  outcrops,  and  these  interfere  with  its, 
use. 

Lower  Freeport  clay. — This  is  not  much  developed,  but  at  one 
locality,  namely,  in  the  vicinity  of  Moxahala,  Perry  County,  the  seam 
is  found  in  the  nature  of  flint-clay,  but  contains  too  much  iron  to  permit 
its  use  for  the  highest  grades  of  ware.  More  often  the  clay  represents 
the  impure  type  so  abundant  in  the  coal-measures. 

Upper  Freeport  clay  and  shale. — This  bed  is  more  important  than 
the  preceding,  since  it  occurs  in  great  quantity  and  more  widely  dis- 
tributed than  the  coal-seam  from  which  it  gets  its  name.  It  assumes 
-a  flinty  phase  at  several  points. 

SECTION  AT  BELLAIRE,  OHIO 

Feet.       Inches.  Feet      Inches. 

Coal,  Waynesburg • —  2 

Shale,  sandy 6 

Shale 12 

Limestone 3 

Concealed 5 

Coal,  blossom,  Little  Waynesburg 

Concealed 14 

Coal,  blossom,  Uniontown 1 

Shale 4 

Sandstone 6 

Shale,  argillaceous 20 

Concealed 32 

Shale 2  }•      127          6 

Sandstone 3 

Shale 3 

Concealed 33 

Calcareous  shale,  with  thin  limestones. . .  21  6 

Coal 4 

Shales,  sandy 13  10 

Coal,  Sewickley      Coal 0  8       J-       27          6 

Shales,  argillaceous.  .  .  6 

Coal 3 

Shale,  argillaceous. 2 

Limestone,  thin  clay  in  center 8 

Limestone,  magnesia-cement  rock 5 

Clay 1 

Limestone 11 

Concealed 11 

Coal,  Redstone,  blossom 2 

Concealed 17  1         t  Q 

Shale 1 

•Coal,  Pittsburgh 7 


Total. 


263 


398 


CLAYS 


Conemaugh  or  Lower  Barren  Measures. — These  contain  vast  deposits 
of  shale,  which  are  extensively  used  for  the  manufacture  of  paving-brick. 
They  are  distributed  through  the  entire  series,  but  about  the  middle 
portion  of  this  division  beds  of  special  prominence  occur,  as  in  the  Sunday 
Creek  Valley.  An  excellent  shale  has  been  found  underlying  the  coal 
at  Bellaire.  Fig.  60  by  White  (Ref.  6)  gives  the  section  of  the  Barren 
Measures  opposite  Steubenville,  Ohio. 

Monongahela  or  Upper  Productive  Measures. — This  series  extends 
from  the  base  of  the  Pittsburg  coal  up  to  the  Cassville.  The  section 
on  page  397,  given  by  I.  C.  White  (Ref.  6),  from  Bellaire,  Belmont 
County,  shows  the  character  of  the  series. 

The  area  of  outcrop  forms  a  narrow,  sinuous  band  extending  in  a. 
northeasterly  direction  from  Gallipolis  to  Steubenville,  and  southward 
from  there  to  beyond  Bellaire.1 

Dunkard  or  Upper  Barren  Measures. — In  Ohio  these  underlie  an 
area  extending  through  the  counties  of  Belmont,  Monroe,  Washington, 
Athens,  Meigs,  and  Gallia. 

Pleistocene 

Pleistocene  clays  are  found  in  all  parts  of  the  State,  but  they  are 
used  chiefly  for  common  brick  and  drain-tile. 

ANALYSES  OF  OHIO  CLAYS 


I. 

II. 

III. 

IV. 

V. 

VI. 

VII. 

Silica  (SiO2)  

76.24 

63.09 

52.52 

61.86 

69.37 

69.79 

56  44 

Alumina  (Al2Oa)  

16.87 

20.17 

31.84 

26.02 

19.08 

19.31 

26  60 

Ferric  oxide  (Fe2O3) 

0  16 

2  12 

0  67 

0  63 

1  26 

2  00 

Lime  (CaO)  
Magnesia  (MgO)  .     ... 

0.50 
trace 

0.50 
0  19 

1.26 
0  19 

0.60 
0.63 



0.47 
0  63 

Potash  (K->O)  

1  -i   ™ 

/O  59 

f  2.14 

3  20 

Soda  (Na2O)   

[1.09 

2.76 

{ 

JO.  31 

1  0.02 

0  26 

Water  (H2O)  

u  , 

f  5.41 

11.68 

9.73 

5.57 

5  09 

7  57 

Moisture 

>  5.14 

\  6  45 

0  69 

0  94 

1  02 

2  48 

Titanium  oxide  (TiO2)     .  . 

1  68 

0  29 

VIII. 

IX. 

X. 

XL 

XII. 

XIII. 

XIV. 

Silica  (SiO2)  

68  13 

66  21 

57  15 

57  10 

49  30 

58  20 

57  28 

20  80 

21.13 

20  26 

21  29 

24  00 

22  47 

21   13 

Ferric  oxide  (Fe2O3) 

1  20 

1  28 

7  54 

7  31 

8  40 

5  63 

8  52 

Lime  (CaO)  .                 .    . 

0  42 

0  51 

0  90 

0  29 

0  56 

0  6° 

5  79 

Magnesia  (MgO)  

0  37 

0  18 

1  62 

1  53 

1  60 

0  9£ 

2  13 

Potash  (K2O)  

2  28 

1  42 

3  05 

3  44 

3  91 

3  Of 

Soda  (NaoO)   

0  27 

0  38 

0  58 

0  61 

0  19 

0  49 

Water  (H2O)  

5  72 

6  29 

5  50 

6  00 

9  40 

6  15 

5  22 

Moisture  

1  00 

1  65 

2  70 

1  30 

1  20 

1  6f 

Titanium  oxide  (TiO2) 

See  U.  S.  Geol.  Surv.,  Bull.  No.  65,  Map  II.  I. 


NORTH  DAKOTA  TO  WYOMING 
ANALYSES  OF  OHIO  CLAYS — Continued 


399 


XV. 

XVI. 

XVII. 

XVIII. 

XIX. 

XX. 

•Silica  (SiO2).  .  .  . 

52  19 

53  38 

44  60 

59  92 

57  80 

51  72 

.Alumina  (A^Oa)   .  . 

14  61 

19  36 

40  05 

27  56 

25  54 

30  10 

Ferric  oxide  (FesOa)  

10  00 

14  86 

0  80 

1  03 

2  51 

1  94 

Lime  (CaO)  

1  48 

0  27 

trace 

0  25 

0  62 

Magnesia  (MgO)  

1  06 

trace 

trace 

0  61 

0  53 

Potash  (K2O)  

trace 

0  67 

2  51 

2  74 

Soda  (NaoO)  

trace 

0  18 

Water  (H2O)  

5.62 

14  23 

9  70 

8  35 

9  95 

Moisture 

12  62 

1  12 

2  25 

1  05 

Titanium  oxide  (TiO2)      •  • 

1  35 

LOCALITIES  OF  THE  ABOVE 


No. 

Locality. 

Geological  Age. 

Uses. 

I 

Haydenville  

Lower  Carboniferous  

Fire-brick 

II. 

Ill 

North  Industry  
Mineral  Point 

Lower  Coal-measures  
Lower  Kittanning 

Paving-brick 
Refractory  wares 

IV 

Darlington 

t(                (( 

Paving-brick 

v 

Roseville  

Stoneware 

VI 

Roseville 

Cooking  ware 

VII 

Steubenville 

Stoneware 

VIII. 
IX 

Akron  
Zanesville 

Lower  Carboniferous  
Lower  Coal-measures.    .  .  . 

Stoneware 
Cooking  ware 

x 

Gloucester 

Cambridge  

XI 

Canton      .              ... 

Lower  Coal-measures  

Paving-brick 

XII. 

Waynesburg  

Middle  Kittanning  
f  Freeport  shale  

Brick 

XIII. 

Zanesville  

XTV 

Northern  Ohio 

Bedford  shale 

Paving-brick 

XV 

North  Industry 

Lower  Carboniferous  

Pa  vin  g-brick 

XVI 

Canton                

(  (                 tt 

YVTT 

Scioto  County 

1  1                 1  1 

Fire-brick 

XVIII 

Salineville        

Fire-brick 

VTV 

East  Palestine 

Upper  Freeport  

Paving-brick 

XX. 

Jefferson  County.  .  .  . 

Sewer-pipe 

Nos.  I-XX  from  Ohio  Geol.  Surv.,  VII.  1893. 

References  on  Ohio  Clays 

1.  Leverett,  F.,  On  the  Significance  of  the  White  Clays  of  the  Ohio 
Region,  Amer.  Geol.,  X,  p.  18,  1893. 

2.  Orton,  E.,  The  Clays  of  Ohio,   their  Origin,  Composition,   and 
Varieties,  Ohio  Geol.  Surv.,  VII,  p.  45,  1893. 

3.  Orton,  E.,  Jr.,  The  Clay-working  Industries  of  Ohio,  Ohio  Geol. 
Surv.,  VII,  p.  69,  1893. 

4.  Prosser,  C.  S.,  Geological  Scale  of  Ohio,  Ohio  Geol.  Surv.,  Bull.  7, 

1905. 

5.  Stevenson,  J.  J.,  Carboniferous  of  the  Appalachian  Basin,  Geol. 
Soc.  Amer.,  Bull.,  XV,  p.  37,  1904. 


400  CLAYS 

6.  White,  I.  C.,  Correlation  Papers,  Carboniferous,  U.  S.  Geol.  Surv.,, 
Bull.  65,  1891. 

7.  See  also  annual  reports  of  inspector  of  mines. 

Oklahoma  Territory  1 

The  rocks  of  the  greater  part  of  Oklahoma  consist  of  deposits  of  red1 
clay-shale.  In  the  eastern  part  of  the  Territory  these  clays  are  of  Penn- 
sylvanian  age,  while  farther  west  they  belong  to  Permian  formations. 
In  the  Osage  Nation,  and  the  counties  bordering  on  the  Arkansas  River, 
there  are  beds  of  gray  and  drab  clay  contained  between  ledges  of  flinty 
limestone  of  Pennsylvanian  and  Permian  age,  while  in  the  Wichita 
Mountains  in  the  southwestern  part  of  the  Territory  there  are  beds  of 
kaolin,  formed  from  the  disintegration  of  granite  and  gabbro  rocks. 
On  the  uplands  in  Beaver  and  Woodward  counties  there  are  deposits 
of  Tertiary  clay,  but  much  of  this  contains  a  considerable  amount  of  lime, 
and  might  not  therefore  be  suited  to  the  manufacture  of  clay-products. 
Dakota  (Cretaceous)  clays  occur  in  the  extreme  northwestern  part  of 
Beaver  County,  and  alluvial  clays  are  found  in  the  river  valleys  in  all 
parts  of  the  Territory. 

The  only  use  that  has  been  made  of  the  clay-deposits  in  Oklahoma 
is  for  the  manufacture  of  brick.  In  nearly  every  small  town  common 
brick  are  made,  chiefly  of  alluvial  clay.  Pressed-brick  plants  are  in 
operation  at  Oklahoma,  Chandler,  Guthrie,  Geary,  Mangum,  El  Reno,, 
and  Anadarko.  On  account  of  the  utilization  of  natural  gas  for  fuel 
at  the  Kansas  brick-yards,  and  consequent  cheaper  cost  of  production, 
much  of  the  brick  used  in  Oklahoma  comes  from  that  State. 

An  analysis  of  clay  from  Stucks  Canyon,  four  miles  west  of  Ferguson,. 
Blaine  County,  yielded : 

Silica  (SiO2) 64. 17 

Alumina  (A1203) ; . . .   14.80 

Ferric  oxide  (Fe2O3) 8. 10 

Lime  (CaO) 1 .34 

Magnesium  carbonate  (MgC03) 27 

Magnesium  sulphate  (MgSO4) 5 .57 

Water  (H2O) 6.54 


Total 100.79 

This  shows  a  curiously  high  percentage  of  magnesium  sulphate. 

1  The  notes  relating  to  this  Territory  have  been  supplied  to  the  author  by 
Professor  C.  N.  Gould.  The  general  geology  of  the  Territory  is  described  in  U.  S. 
Geol.  Surv.,  Water-supply  and  Irrigation  Bull.  No.  148,  by  C.  N.  Gould. 


NORTH  DAKOTA  TO  WYOMING  401 


Pennsylvania 

The  geologic  formations  of  Pennsylvania  range  from  the  pre-Cam- 
brian  crystalline  rocks  to  those  of  Pleistocene  age. 

In  the  western  part  of  the  State,  except  the  northwestern  counties, 
the  rocks  are  nearly  all  of  Carboniferous  age,  the  beds  being  bent  into 
a  series  of  gentle  folds;  but  often  the  exposure  of  the  lower  or  older 
beds  is  due  partly  to  the  overlying  strata  having  been  worn  away. 

To  the  eastward  the  rocks  become  highly  folded  in  the  central  coun- 
ties of  the  State,  so  that  the  strata  often  have  a  very  steep  dip,  and  not 
only  the  Carboniferous,  but  also  the  lower-lying  Devonian  and  Silurian 
formations  are  exposed,  giving  rise  to  bands  which  extend  in  a  general 
northeast-southwest  direction. 

On  the  eastern  edge  of  the  State  there  is  a  fringe  of  coastal-plain 
formations,  but,  with  the  exception  of  the  Columbia  loams,  they  have 
little  value  in  Pennsylvania.  North  of  the  terminal  moraine  the  drift- 
clays  are  wide-spread. 

Residual  Clays 

These  might  occur  at  almost  any  point  in  the  area  lying  south  of 
the  terminal  moraine,  but  the  deposits  of  greatest  economic  value  are 
those  found  in  the  Great  Valley,  along  the  line  of  which,  as  well  as  in 
the  South  Mountain  region,  there  are  a  number  of  deposits  of  white 
and  variegated  clays  (PL  XXXV,  Fig.  1).  These  have  been  derived 
from  the  decomposition  of  hydromica  slates,  which  are  interstratified 
with  Ordovician  limestones  and  quartzites,  talcose  slates,  and  lime- 
stones of  Cambrian  age.  Of  recent  years  these  white  clays  have  been 
much  worked  for  paper  manufacture,  and  to  a  less  extent  for  tile  and 
fire-brick. 

The  most  productive  localities  have  been  South  Mountain,  Cumber- 
land County;  Mertztown,  Berks  County;  Ore  Hill,  near  Roaring  Springs 
in  Blair  County,  etc. 

A  number  of  localities  are  mentioned  in  the  reports  of  the  Second 
Pennsylvania  Geo  ogical  Survey,1  but  many  of  these  are  no  longer 
worked.  More  recently  they  have  been  described  by  T.  C.  Hopkins.2 

A  second  type  of  white  residual  clay  or  kaolins  are  those  of  Delaware 
and  Chester  counties,  which  have  been  formed  by  the  weathering  of 

1  Second  Pa.  Geol.  Surv.,  Kept.  C4,  pp.  137,  272,  275,  277,  279,  325,  340,  and 
Kept.  CC,  p.  203. 

2  Kept.  Penn.  State  College  for  1898,  1899,  and  1900. 


402  CLAYS 

pegmatite  veins.  These  have  been  worked  near  Kaolin  P.  0.,  Brandy- 
wine  Summit,  etc.,  but  the  output  is  less  than  formerly,  because  the 
deposits,  being  the  product  of  weathering,  have  in  some  cases  been 
exhausted  with  depth. 

These  kaolins  are  washed  for  the  market,  and  in  some  instances  the 
siliceous  material  left  behind  is  used  for  silica  brick. 

Silurian  and  Devonian  Shales 

The  vast  beds  of  shale  occurring  in  these  formations  in  the  eastern 
and  south-central  portions  of  Pennsylvania  should  afford  an  excellent 
field  for  exploitation  by  the  clay-worker. 

The  Devonian  is  found  overlying  large  areas  in  northwestern  Penn- 
sylvania and  may  be  of  value,  but  in  the  northeastern  counties  the 
beds  are  often  too  siliceous. 

To  the  south  and  southeast  the  Silurian  and  Devonian  formations 
appear  as  a  series  of  bands  in  Lackawanna,  Luzerne,  Carbon,  Cumber- 
land, Snyder,  Juniata,  Perry,  and  other  counties,  and  the  shale-beds 
found  in  them  are  worked  at  several  localities  for  the  manufacture  of 
both  building-  and  paving-brick.  The  Clinton  shales  have  been  dug  for 
brickmaking  in  Laurel  ton  and  Hartleton  townships  of  Union  County; 
the  Mauch  Chunk  shales  at  Pine  Grove,  Williamsport,  and  Sandy  Run  ; 
and  the  Hudson  River  shale  at  Reading. 

Carboniferous 

To  the  clay-worker  this  is  the  most  important  group  of  formations 
occurring  in  Pennsylvania,  for  it  includes  a  wide  range  of  plastic  mate- 
rials, from  saridy  shales  up  to  the  highest  grades  of  fire-clay.  Unfor- 
tunately, no  detailed  systematic  study  of  the  shales  and  fire-clays  of 
the  entire  Carboniferous  area  of  Pennsylvania  has  ever  been  undertaken, 
although  many  scattered  references  to  them  are  given  in  the  reports 
of  the  Pennsylvania  Geological  Survey,  and  Hopkins  has  treated  those 
of  Western  Pennsylvania  in  some  detail.  The  various  references  are 
found  on  p.  414.  The  occurrences  are  here  taken  up  in  regular  order, 
beginning  with  the  oldest. 

Pottsville.— This  member  of  the  Carboniferous  is  composed  chiefly 
of  sandy  beds,  as  sandstones  and  conglomerates,  but  there  are  several 
beds  of  shale  and  coal.  The  latter  is  often  underlain  by  shale  and  in 
some  instances  fire-clay. 

Mercer  or  Alton  fire-clay. — The  Upper  Mercer  coal  is  said  to  be  under- 
lain by  a  fire-clay  in  Elk,  Butler,  Huntington,  McKean,  and  Cameron 


PLATE  XXXV 


FIG.  1. — Kaolin-deposit  at    Upper    Mill,  Mt.  Holly  Springs,  Pa.      (After  Hopkins, 
Clays  of  Pennsylvania,  Pt.  Ill,  p.  18.) 


FIG.  2. — White  sedimentary   clay,   Aiken   area,   S.  C. 

Surv.,  Bull.  1,  1904.) 


(After  Sloane,  S.  C.  Geol. 


•103 


NORTH  DAKOTA  TO  WYOMING 


405 


Bounties,  while  in  Beaver,  Lawrence,  and  Mercer  counties  shale-beds 
have  been  noticed,  but  no  fire-clays. 

Sharon  upper  coal  fire-clay.  —  In  Elk  County  a  bed  of  fire-clay  is 
said  to  be  often  associated  with  the  upper  Marshburg  coal-bed,  and  has 
been  worked  in  Benezette  township.  Another  is  also  found  in  Mercer 
County. 

Savage  Mountain  fire-clay.  —  This  clay  is  of  importance  in  Somerset 
County,  and  while  not  of  the  highest  grade  is  said  to  have  given  excel- 
lent satisfaction  for  coke-oven  brick. 

Allegheny  or  Lower  Productive  Measures.—  These  contain  a  number 
•of  important  beds  of  fire-clay  and  coal  in  western  and  western-central 
Pennsylvania.  The  formation  rests  on  the  Pottsville  sandstone,  and 
extends  to  the  top  of  the  upper  Freeport  coal. 

Along  the  upper  Ohio  River,  where  the  section  is  specially  impor- 
tant, the  following  beds  are  seen:1 


Oto4 

2  to  4 

1  to  4 

Kr.  ,    ~A 

50  to  70 

0  to  2 

0  to  5 


SECTION  ALONG  THE  UPPER  OHIO  RIVER  IN  PENNSYLVANIA 

1.  Upper  Freeport  coal;  "  Four-foot"  or  "Hookstown 

vein" 

2.  Fire-clay 

3.  Limestone 

4.  Shale  and 

5.  Sandstone 

6.  Lower  Freeport  coal  (usually  absent) 

7.  Fire-clay 

8.  Limestone  (sometimes  present)  ........ 

9.  Sandstone,  or  sandstone  and  shale 

10.  Darlington;  "Block  vein"  at  Smith's  Ferry 

11.  Fire-clay 

12.  Black  slate  with  iron  nodules  ....... 

13.  Lower  Kittanning  coal;  "  Sulphur  vein" 

14.  Fire-clay 

15.  Sandstone! 

16.  Shale          )•  •;  ................  ; 

17.  Limestone,  ferriferous,  "  Vanport  limestone" 
Black  shale 

f  Fire-clay 

18.  \  Sandy  shale 
[  Fire-clay 

19.  Clarion  coal 

20.  Fire-clay 

21.  Sandstone  ..... 

22.  Shale 

23.  Brookville  coal 

24.  Fire-cla 


70  to  90 

1  to  2 
4 

20  to  30 

2  to  3 

6  to  10J 


1  to  20 
15 

20 

1± 

4  to  6 
23 
25 

6 

4 


,  ™ 


,  nn 


Brookville  clay. — The  Brookville  coal  is  underlain  by  a  persistent 
and  widely  distributed  clay.  In  the  upper  Ohio  and  Beaver  River 
region  it  is  irregular  and  often  impure,2  but  in  other  regions  is  more 

1  U    S.  Geol.  Surv.,  Bull.  225,  p.  467,  1904. 

2  R.  R.  Hice,  Trans.  Amer.  Cer.  Soc.,  Vol.  VII,  Pt.  II,  p.  251. 


406  CLAYS 

promising.  It  is  said  to  have  been  used  for  fire-brick  manufacture  at 
Sandy  Ridge,  Blueball,  Woodland,  and  Hope  Station,  Clearfield  County; 
Benezette,  Elk  County;  Parkville,  Jefferson  County;  Queens  Run  and 
Farrandsville,  Clinton  County.  It  has  also  been  mined  for  many  years 
at  Blacklick,  Indiana  County,  but  has  to  be  handpicked  to  remove  the 
ferruginous  concretions. 

In  Fayette  County  it  is  a  flint-clay,  and  has  been  extensively  used 
for  fire-brick  manufacture.1  At  Brookville,  Jefferson  County,  the  coal  is 
underlain  by  15  feet  of  fire-clay,  but  only  the  upper  part  appears  to  be- 
of  high  purity.2 

Clarion  clay. — This  clay  underlies  the  Clarion  coal,  and  is  said  to 
be  of  good  quality  at  most  localities.  It  has  been  used  at  Bolivar  for 
fire-brick,3  and  has  also  been  mined  on  Brady's  Run,  Beaver  County, 
but  does  not  appear  to  have  been  much  developed  in  that  locality,  even 
though  purer  than  the  Lower  Kittanning  clay.  This  is  thought  to  be- 
due  to  the  fact  that  it  is  less  accessible  than  the  Kittanning  clays,  and 
because  it  takes  a  longer  time  to  weather,  and  is  therefore  more  difficult 
to  wash  for  pottery  purposes.4 

Other  important  deposits  have  been  reported  from  near  Kittanning,5 
where  they  have  been  worked  for  buff  brick.  The  clay  is  also  present 
at  Johnstown,  and  Ben's  Run,  Cambria  County,  and  Pinkerton  Point,. 
Somerset  County. 

Ferriferous  coal  under-clay. — According  to  the  Pennsylvania  Survey 
reports  6  a  deposit  of  fire-clay  occurs  between  the  Ferriferous  coal-bed 
and  the  Buhrstone  iron  ore  in  Armstrong  County.  It  is  probably  purely 
local  and  of  doubtful  value. 

Lower  Kittanning  fire-clay. — Underlying  the  Lower  Kittanning  coal 
there  is,  in  many  localities,  an  important  bed  of  fire-clay  which  is  often 
more  vaulable  than  the  coal,  and  has  been  extensively  used  for  the? 
manufacture  of  clay-products.  At  times  there  is  an  interval  of  as  much 
as  30  or  50  feet  between  this  clay  and  the  ferriferous  limestones,  but 
at  others  the  former  rests  immediately  on  top  of  the  latter. 

White7  states  that  "eastward  from  the  Allegheny  River  this  clay 

1  Geologic  Atlas,  U.  S.,  Folio  82;  U.  S.  Geol.  Surv.,  p.  20. 

2  For  other  references  to  this  clay,  see  reports  of  Pa.  Geol.  Surv.  as  follows:: 
HH,  p.  146;  H,  pp.  120,  124,  134,  225;   Q3,  pp.  27,  81,  111,  134,  etc. 

3  Second  Penn.  Geol.  Surv.,  Kept.  K3,  p.  43. 

4R.  R.  Hice,  Trans.  Amer.  Cer.  Soc.,  Vol.  VII,  Pt.  II,  p.  253. 

6  Pa.  Geol.  Surv.,  Kept.  H  5,  p.  245. 

•  H5,  pp.  239,  249. 

7U.  S.  Geol.  Surv.,  Bull.  65,  p.  172,  1891. 


NORTH   DAKOTA  TO  WYOMING  407 

does  not  appear  to  be  very  important,  but  westward  from  that  point 
it  is  generally  present,  and  attains  its  maximum  development  along  the 
Beaver,  and  westward  from  there  down  the  Ohio.  It  is  much  used  by 
the  pottery  and  tile  works  at  New  Brighton,  East  Liverpool,  etc." 

Hice  l  states  that  in  the  Upper  Ohio  and  Beaver  River  region  it  is 
persistent,  quite  constant  in  quality,  and  has  a  good  roof,  and,  on  account 
of  the  extent  to  which  it  has  been  worked  in  this  area,  is  sometimes  called 
the  "New  Brighton  Clay." 

The  Lower  Kittanning  clay  appears  to  vary  from  5  to  15  feet  in 
thickness,  and  often  consists  of  two  portions,  an  upper  soft  clay  and 
a  lower  hard  clay.  White  states  that  the  latter  is  used  for  fire-brick,2 
but  Woolsey  claims  that  this  is  the  more  siliceous  portion.3  This  clay- 
bed  has  been  extensively  used  in  Beaver  County  to  supply  the  factories 
of  pottery,  hollow  ware,  fire-brick,  and  paving-brick.  It  is  not  to  be 
understood,  of  course,  that  the  same  grade  is  used  for  all  purposes,  but 
that  different  parts  of  the  deposits  are  used,  either  alone  or  mixed  with 
other  clays. 

The  sections  given  in  Fig.  61  represent  the  position  of  the  Lower 
Kittanning  clay  at  several  localities.  The  Second  Pennsylvania  Geo- 
logical Survey  reports  refer  to  it  in  the  counties  of  Armstrong,4  Beaver,5 
Fayette,  and  Westmoreland.6 

Middle  Kittanning  clay. — This  bed,  known  also  as  the  Darlington, 
is  sometimes  found  under  the  coal  of  the  same  name,  and  has  been 
noted  by  the  geologists  of  the  Second  Pennsylvania  Geological  Survey  in 
Allegheny,  Armstrong,  Tioga,  Blair,  and  Beaver  counties,  but  was  in- 
correctly referred  by  them  to  the  Upper  Kittanning.  It  does  not 
appear  to  be  an  important  bed.  According  to  Hice  7  it  is  worked  on 
Brady's  Run  in  Beaver  County,  and  is  there  partly  a  flint-clay.  The 
clay  is  not  uniform  in  thickness,  and  of  more  variable  quality  than  the 
Lower  Kittanning. 

Woolsey  8  states  that  in  the  Ohio  Valley  the  bed  is  a  very  persistent 
one,  but  rarely  worked  on  account  of  the  iron  nodules  which  it  contains. 

Upper  Kittanning  clay. — There  seems  to  be  a  difference  of  opinion 

'L.  c. 

2L.  c.,  p.  172. 
3L.  c.,  p.  470. 

4  H5.  See  also  Hopkins,  Clays  of  Western  Pennsylvania,  Ann.  Kept.  Pa.  State 
College,  1897,  p.  33. 

6  Q,  pp.  58,  59,  190,  193,  195,  205,  and  215. 

6  K3,  p.  40. 

7  L.  c. 

•*  L.  c.,  p.  472. 


408 


CLAYS 


regarding  the  occurrence  of  a  clay-deposit  at  this  horizon.     While  it 
may  be  present,  it  is  in  general  of  no  great  value. 

Lower  Freeport  clay. — Above  the  Kittanning  series  come  the  Free- 
port  series,  consisting  of  two  coals  and  underlying  fire-clays,  and  twoi 
limestones  which  underlie  the  clays. 


Fire  clay 


Fire  clay 


Lower   * 

Kittanning> 

tire  clay  I 


Ferriferous! 
limestone  [ 


Fire  clay 


Coal 


Coal 
Concealed 


Coal 
Fire  clay 


Ferriferous' 
limestone  f 


FIG.  61. — Vertical  sections  near  New  Brighton,  Pa.     (After  Hopkins.) 

The  Lower  Freeport  clay  does  not  appear  to  have  assumed  much 
importance,  and  little  mention  has  been  made  of  it  in  print.  In  the 
Upper  Ohio  and  Beaver  River  region  it  is  generally  quite  thin,  but  in 
places  reaches  a  workable  thickness,  and  at  one  point  on  Brady's  Run 


0> 

§    § 
tg     -" 

"d 

£3 


I? 

•5  3 


18 


NORTH   DAKOTA  TO  \\YOMING  411 

22  feet  have  been  mined.  It  has  been  used  for  low-grade  fire-brick, 
but  usually  carries  too  many  impurities  to  allow  its  use  for  refractory 
purposes.  It  is  generally  thoroughly  vitrified  at  cones  6  and  7.1  "On 
Block  House  Run,  Beaver  County,  it  has  been  worked  for  sewer-pipe."2 

Upper  Freeport  limestone  clay  or  Bolivar  fire-clay. — This  limestone 
is  quite  generally  distributed  in  western  Pennsylvania,  but  when  absent 
or  but  slightly  represented  there  is  found  at  its  horizon  a  bed  of  high- 
grade  fire-clay  known  as  the  Bolivar  clay,  and  long  mined  at  the  locality 
of  the  same  name  in  Westmoreland  County.  It  represents  a  non-plastic 
or  flint-clay,  which  has  been  extensively  used  in  fire-brick  manufacture. 
On  the  Ohio  and  Beaver  rivers  this  seems  to  be  replaced  by  a  less  refrac- 
tory shale.  At  some  points  the  Bolivar  clay  and  upper  Freeport  clay 
above,  and  for  which  it  has  sometimes  been  mistaken,  may  lie  close 
together,  as  at  Salina,  Westmoreland  County.  It  is  also  known  in  Fay- 
ette,  Indiana,  and  other  counties  of  western  Pennsylvania. 

Upper  Freeport  clay. — This  underlies  the  Upper  Freeport  coal,  but 
is  often  more  persistent  than  its  coal-bed.  In  the  Ohio  Valley  region 
it  is  found  at  several  points,3  and  has  been  used  for  fire-brick,  being  some- 
times mixed  with  the  Lower  Kittanning  clay.  It  has  also  been  worked 
around  Bolivar  and  Salina. 

Conemaugh  Series  or  Lower  Barren  Measures. — These  consist 
largely  of  shales  and  sandstones  with  some  limestones,  the  shales  pre- 
dominating in  the  upper  beds  of  the  section  and  the  sandstones  in  the 
lower.  They  extend  from  the  Upper  Freeport  coal  to  the  base  of  the 
Pittsburg  coal,  and  their  general  character  can  be  well  seen  from  the 
accompanying  section  (Fig.  62).  They  form  the  surface  over  a  large  area 
in  Allegheny,  Armstrong,  Butler,  Beaver,  and  Westmoreland  counties.4 

Although  their  distribution  is  referred  to  in  the  various  county  reports 
of  the  Second  Pennsylvania  Geological  Survey,  their  possibility  for  the 
manufacture  of  clay-products  was  not  considered.  Their  importance 
was,  however,  well  set  forth  in  a  report  issued  by  the  Pennsylvania  State 
College.5  In  this  Affelder  states  that  at  Pittsburg,  where  320  feet  of 
strata  of  the  Conemaugh  formation  are  exposed  between  the  level  of 
the  Monongahela  River  and  the  outcrop  of  the  Pittsburg  coal  near  the 
hilltop,  almost  all  of  the  rock  is  shale,  most  of  which  is  well  adapted  to 
the  manufacture  of  brick.  The  color  is  variable,  but  most  of  the  beds 
are  red-burning.  Fire-clays  do  not  appear  to  be  abundant  in  the  Cone- 
maugh, but  some  low-grade  ones  have  been  found  and  used  to  advan- 

1  Hice,  1.  c.  2  Woolsey,  1.  c.,  p.  472.  3  Ibid. 

4  See  map,  U.  S.  Geol   Surv.,  Bull.  65. 

5  The  Clays  of  Western  Pennsylvania,  Ann.  Kept.  Pa.  State  College,  1897  p.  137. 


412 


CLAYS 


Pittsburg  coal. 

Concealed 

Limestone.  .  .  . 

lijfj 

Hvtei^i 

Shales,  variegated. 

Limestone 

Red  shale fiJl^-Iltf ~° 

Concealed ~o 

Sandstone,  Morgantown 

Coal,  Elk  Lick 

Shales,  variegated EL    |^"j^i 50 

Limestone J    I 

Shales,  variegated |jf 4f|"i 

Limestone,  Ames *     ! 

Coal,  crinoidal 

Red  and  variegated  shale I  ^  30 

Sandy  shales  and  shaly  sandstone i?S^i-^-_-^-j  50   at 

Coal,  Bakerstown ^^^.-'ff.  3 

Shales  and  sandstone , \ 

Limestone,  Upper  Cambridge. 

Sandstone,  massive .•.:-.-:•••.•....    50 

Limestone,  Lower  Cambridge. 

Shales |!4fMlftj  10' 

Coal,  Masontown 

Shales =l^Mrfao' 

Sandstone,  Mahoning ..•-.•:.-•.•••..     100 


FIG.  62. — Section  of  Upper  Barren  Measures  in  Pittsburg  region,  Penn. 
(.After  I.  C.  White,  U.  S.  Geol.  Surv.,  Bull.  65.) 


NORTH  DAKOTA  TO  WYOMING 


413 


tage  for  the  manufacture  of  building-  and  paving-brick,  as  at  Harmon- 
ville.  Of  the  57  yards  listed  in  the  report  just  referred  to  over  two 
thirds  use  shale  wholly  or  in  part. 

Monongahela  Series  or  Upper  Coal-measures. — These  show  their 
greatest  development  in  southwestern  Pennsylvania,  and  while  the 
shale-deposits  do  not  appear  from  published  reports  to  be  as  abundant 
as  in  West  Virginia,  still  occasional  thick  beds  of  shale  occur. 

An  important  clay-parting,  6  to  10  inches  thick,  is  found  in  the  Pitts- 
burg  coal-bed,  and  is  used  in  the  Monongahela  Valley.  It  has  to  be 
removed  in  mining  the  coal  and  can  hence  be  made  a  source  of  profit. 
The  shale  over  the  coal  has  been  used  at  Fayette  City  for  making  red 
brick,  while  at  Pittsburg  the  shale  of  this  group  is  used  for  making  brick 
and  terra-cotta  lumber. 

Pleistocene  Clays 

These  are  distributed  over  most  of  the  State.  They  are  of  superficial 
character  and  rarely  of  great  extent.  Around  Philadelphia  the  Col- 
umbian loams  have  for  many  years  been  worked  for  both  common  and 
pressed  brick. 

In  western  Pennsylvania  clays  are  found  under  many  river  terraces, 
notably  along  the  Allegheny,  Monongahela,  Beaver,  Ohio,  and  Youghio- 
gheny.1  Along  the  Ohio  and  Beaver  rivers  there  are  three  well-marked 
terraces,  lying  respectively  30-50, 150,  and  200-250  feet  above  the  river- 
level.  Clays,  which  are  dug  in  the  highest  and  lowest  of  these,  are  used 
for  brick  and  earthenware,  and  excellent  results  are  sometimes  also 
obtained  by  mixing  these  with  shales. 

ANALYSES  OF  PENNSYLVANIA  CLAYS 


I. 

II. 

III. 

IV. 

V. 

VI. 

VII. 

VIII. 

Silica  (SiO2) 

73  30 

59  83 

46  26 

51.72 

44  04 

55  21 

45  65 

58  75 

Alumina  (A^Oa)   .  . 

17  43 

26  96 

36  25 

21  73 

39  44 

31  18 

34  73 

25  17 

Ferric  oxide  (Fe2O3).  .  .  . 
Lime  (CaO) 

0.37 
0  02 

1.98 
0  11 

1.64 
0  19 

f  FeO 
17.87 

0  06 

FeO 
0.94 
0  07 

J0.07 
0  18 

3.54 
0  11 

/FeO 
J2.19 
0  71 

Magnesia  (MgO) 

1  28 

0  50 

0  32 

2  37 

0  11 

0  11 

0  61 

0  93 

Potash  (KaO) 

2  99 

0  94 

1  69 

}  A 

Soda  (Na2O) 

0  17 

0  24 

0  85 

f  4.58 

0.72 

0.23 

5.75 

3.53 

Water  (H2O) 

4  68 

9  56 

13  54 

J 

13  02 

8  11 

Titanium  oxide  (TiO2) 

0  87 

1  05 

Ignition          

10.78 

14.13 

9.65 

Sulphur  trioxide  (SOs) 

trace 

Organic  and  loss 

0  23 

Mang  dioxide  (MnO2) 

trace 

*  For  references  see  foot  of  table,  p.  414. 


Hopkins,  Ann.  Rep.  Pa.  State  College,  1897,  p.  144. 


414 


CLAYS 

ANALYSES  OF  PENNSYLVANIA  CLAYS. — Continued 


IX. 

X. 

XI. 

XII. 

XIII. 

XIV. 

XV. 

XVI. 

Silica  (SiO2)  
Alumina  (A^Oa).  .  .. 

50.37 
32  89 

62.89 
21  49 

51.92 
31  64 

55.33 

27  84 

46.16 
26  97 

67.78 
16  29 

61.81 
27  18 

54.09 

10    OK 

Ferric  oxide  (Fe2O3).  .  { 
Lime  (CaO) 

FeO 
1.64 
0  31 

FeO 
1.81 
0  38 

FeO 
1.13 
0  03 

FeO 
2.91 
0  58 

7.21 
2  21 

4.57 
0  60 

6.96 
2  00 

9.84 
0  72 

Magnesia  (MffO)  . 

0  35 

0  56 

0  44 

0  75 

1  52 

0  72 

i   50 

1  55 

Potash  (K2O)                \ 

Soda  (Na2O)                 } 

0.29 

2.52 

0.40 

3.91 

3.24 

2.00 



3.31 

Water  (H2O)  

7.58 

13.49 

7.49 

11.22 

6  34 

2  20 

Titanium  oxide  (TiO2).  . 

1.03 
13.76 

1.82 

1.16 

1.14 

JC02 

0.74 
1 

0.78 

8  98 

Moisture  

1.16 

\     .45 

/ 

I.  Mount  Holly,  white  mixed  clay,  residual. 

II.  Conshohqcken,  parti-colored  clay,  residual. 

III.  Brandywine  Summit,  residual. 

IV.  Wilmarth  Station,  Mercer  fire-clay. 

V.  Fletcher  mine,  Elk  County,  Sharon  fire-clay. 

VI.  Somerset  County,  Mt.  Savage  fire-clay. 

VII.  Sandyridge,  Clearfield  County,  Brookville  under-clay. 

VIII.  Kittanning,  Clarion  coal  under-clay. 

IX.  Allegheny  Furnace,  ferriferous  coal  under-clay. 

X.  New  Brighton,  Kittanning  lower  coal  under-clay. 

XI.  Salina,  Kier  Bros.,  Bolivar  under-clay,  flint-clay. 
XII.  plastic  clay. 

XIII.  New  Brighton,  Mendenhall  &  Chamberlain,  terrace-clay. 
XVI.  Elverson  &  Sherwood,  terrace-clay. 

XV.  Allegheny,  Allegheny  Brick  Co.,  analysis  of  brick. 

XVI.  Butler,  Butler  Brick  and  Tile  Co. 

Nos.  I-XVI  from  U.  S.  Geol.  Surv.,  Prof.  Pap.  11. 

In  other  parts  of  the  State  many  local  deposits  are  employed  for 
common  and  pressed  brick.1 

References  on  Pennsylvania  Clays 

1.  Ashburner,  C.  A.,  Report  on  the  Brandywine  Summit  Kaolin  Bed, 
Delaware  County,  Geol.  Surv.  Pa.,  Ann.  Kept,  for  1885,  p.  592,  1886 

2.  Hice,  R.  R.,  The  Clays  of  the  Upper  Ohio  and  Beaver  River  Region, 
Trans.  Amer.  Ceram.  Soc.,  VII,  Pt.  II,  p.  251,  1905. 

3.  Hopkins,  T.  C.,  Feldspars  and  Kaolins  of  Southeastern  Pennsyl- 
vania, Franklin  Inst.  Jour.,  CXLVIII,  p.  1, 1899. 

4.  Hopkins,  T.  C.,  Fire-clays,  Mines  and  Minerals,  XIX,  p.  53,  1S9S. 

5.  Hopkins,  T.  C.,  Clays  and  Clay  Industries  of  Pennsylvania,  Pt. 
Ill;   Clays  of  the  Great  Valley  and  South  Mountain  Areas,  Pa.  State 
Coll.,  Ann.  Rept.,  1899-1900,  Appendix,  45  pp. 

6.  Hopkins,  T.  C.,  Clays  and  Clay  Industries  of  Pennsylvania,  Pt.  II; 
Clays    of  Southeastern  Pennsylvania  (in  part),  Pa.  State  Coll.,  Ann. 
Rept.,  1898-99,  Appendix,  76  pp.,  1900. 

1  Many  localities  are  noted  in  Prof.  Paper  11,  U.  S.  Geol.  Surv.,  pp.  235-238. 


NORTH  DAKOTA  TO  WYOMING  415 

7.  Hopkins,  T.  C.,  A  Short  Discussion  of  the   Origin  of  the  Coal- 
measure  Fire-clays,  Amer.  Geol.,  XXVIII,  p.  47,  1901;  also  Mines  and 
Minerals,  XXII,  p.  296,  1902. 

8.  Hopkins,  T.  C.,  The  White  Clays  of  Southeastern  Pennsylvania, 
Eng.  and  Min.  Jour.,  LXX,  p.  131,  1900. 

9.  Hopkins,  T.  C.,  Clays  and  Clay  Industries  of  Pennsylvania,  Pt.  I; 
Clays  of  Western  Pennsylvania  (in  part),  Pa.  State  Coll.,  Ann.  Rept.  for 
1897,  Appendix,  pp.  1-183,  1898. 

10.  Platt,  F.,  Tests  of  Fire-brick,  Pa.  Geol.  Surv.,  Rept.  MM,  p.  270. 

11.  Wright,  G.  F.,  The  Age  of  the  Philadelphia  Brick-clay  (Pennsyl- 
vania), Science,  n.  s.,  iii,  p.  242,  1896. 

12.  Many  analyses  in  Penn.  Geol.  Surv.,  Rept.  MM,  p.  257,  et.  seq. 

13.  Scattered  notes  in  Reports  of  Sec.  Penn.  Geol.  Surv.,  especially 
H4,  H5,  C4,  C5. 

Rhode  Island 

This  State  has  very  limited  clay  resources.  Glacial  clays  are  known 
at  a  few  points  around  Narragansett  Bay,  but  the  principal  occurrence 
is  found  in  the  town  of  Barrington,  where  the  deposits  of  bluish-gray, 
sometimes  sandy  clays  are  worked  for  the  manufacture  of  common  brick. 

References  on  Rhode  Island  Clays 

1.  Woodworth,  J.  B.,  Shaler,  N.  S.,  Marbut,  C.  F.,  The  Glacial  Brick- 
clays  of  Rhode  Island  and  Southeastern  Massachusetts,  U.  S.  Geol. 
Surv.,  17th  Ann.  Rept.,  Pt.  I,  p.  557,  1896. 

South  Carolina 

The  northwestern  part  of  the  State  is  underlain  by  crystalline  rocks, 
which  extend  to  the  edge  of  the  coastal  plain,  the  line  of  division  passing 
a  short  distance  southeast  of  Chesterfield  and  Camden,  through  Columbia 
and  west  of  Aiken. 

Residual  Clays 

These  are  to  be  sought  for  throughout  the  crystalline  belt,  and  are 
usually  impure.  No  kaolins  are  reported,  but  many  of  the  white-burn- 
ing sedimentary  clays  of  the  coastal  plain  are  incorrectly  termed  such. 

Coastal-plain  Clays 

The  formations  of  this  area  range  from  Potomac  to  Columbian  in 
age,1  and  consist  of  clays,  loams,  and  marls.     Of  these  the  Potomac 

barton.  U.  S.  Geol.  Surv..  Bull.  138. 


416 


CLAYS 


beds  are  by  far  the  most  important,  outcropping  in  a  belt  from  4  to  5 
miles  wide,  reaching  from  Augusta,  Ga.;  through  Aiken  south  of  Lexing- 
ton and  through  Columbia  to  Camden  and  Cheraw.1  This  contains 
lenses  of  white  clay  which  are  worked  at  Aiken,  Columbia,  Sievern, 
and  other  points.  The  clay  usually  has  to  be  washed  and  is  sold 
chiefly  to  paper  manufacturers.  The  Eocene  deposits  to  the  southeast 
of  the  Potomac  area  also  carry  clays  of  value.  These  deposits  have 
recently  been  described  in  some  detail  by  the  South  Carolina  State 
geologist.2 

The  chemical  and  physical  properties  of  a  number  of  these,  taken 
from  this  report,  are  given  in  the  accompanying  table. 

ANALYSES  OF  SOUTH  CAROLINA  CLAYS 


I. 

II. 

III. 

IV. 

V. 

Silica  (SiO2)  

44.23 

43.18 

44.11 

45  69 

42  30 

Alumina,  (AI>Oa) 

38  98 

37  36 

38  19 

37  47 

36  94 

Ferric  oxide  (Fe2O3)   •  •  . 

0  77 

0  91 

1  55 

1  01 

2  64 

Lime  (CaO) 

0  03 

0  14 

trace 

0  80 

Magnesia  (MgO)  .  . 

0  07 

0  50 

trace 

0  78 

Potash  (K2O) 

0  26 

2  00 

0  50 

0  08 

Soda  (Na2O) 

0  55 

0  53 

0  69 

Titanium  oxide  (TiO2).  « 

0  85 

1  30 

1  44 

Ignition 

13  58 

14.32 

13  37 

13  98 

15  43 

VI. 

VII. 

VIII. 

IX. 

X. 

Silica  (SiO2) 

79  40 

53  19 

54  40 

52  46 

52  41 

Alumina  (A12O3)  
Ferric  oxide  (Fe2O3)  
Lime  (CaO)                

10.70 
2.57 
0  58 

33.41 
1.67 
0  10 

30.14 
2.10 
0  46 

26.81 
1.79 
0  81 

21.14 
12.02 
1  04 

Magnesia  (MgO)  
Potash  (K2O)                

1.05 
1.21 

0.25 
0  66 

0.54 
0  87 

0.33 

0.56 
0  95 

Soda  (Na->O) 

0.23 

0  12 

0  12 

1   12 

Titanium  oxide  (TiO2)  
Ignition           

0.55 
3.94 

0.37 
10.63 

11.37 

14  44 

1.47 
8.95 

I.  Immaculate  Kaolin  Co.,  Langley. 
II.  Sterling  Kaolin  Co.,  near  Warren ville. 

III.  J.  Brodie,  12  miles  north  of  Aiken. 

IV.  Imperial  Kaolin  Co.,  Sievern. 

V.  Carolina   Fire-brick  Co.,  east  of  Killian. 
VI.  A.  W.  Suder,  Clarendon  County. 
VII.  Dents'  Pond. 
VIII.  A.  B.  Osborne,  Union  County. 
IX.  R.  Hamilton,  Jonesville. 
X.  Dr.  Parker,  Edgefield. 


1  Barton,  U.  S.  Geol.  Surv.,  Bull.  138,  p.  208. 

2  E.  Sloan,  S.  C.  Geol.  Surv.,  Series  IV,  Bull.  I,  1904. 


PLATE  XXXVII 


FIG.  1. — Beds  of  Cretaceous  fire-clay,  southwest  of  Rapid  City,  S.    Dak.     (Aftei 
Todd,  S.  Dak.  Geol.  Surv.,  Brll.  3,  p.  113,  1902.) 


General  view  of  valley  at  Thurber,  Tex.,  underlain  by  paving-brick  shale. 
(Photo  by  H.  Ries.) 

417 


NORTH  DAKOTA   TO  WYOMING  419 

South  Dakota 

Very  little  information  has  been  published  regarding  the  clays  and 
shales  of  this  State,  and  it  is  difficult  to  discuss  them  by  formations,  as 
has  been  done  with  most  of  the  other  States. 

Aside  from  scattered  references,  the  best  and  most  recent  informa- 
tion is  that  given  by  J.  E.  Todd,1  from  which  most  of  the  facts  below  are 
taken. 

Clays  abound  in  many  parts  of  the  State,  the  most  important  deposits 
being  found  in  the  Cretaceous,  which  is  largely  composed  of  clay-  or 
shale-deposits,  but  clays  of  the  lower  grades  are  not  wanting  in  the 
Pleistocene  formations.  None  appear  to  have  been  noted  from  the 
Carboniferous.  It  seems  likely  that,  owing  to  the  absence  of  local  de- 
mand, distance  from  important  markets,  and  in  some  cases  remoteness 
of  the  deposits  from  railroads,  the  development  of  the  beds,  unless  of 
high  grade,  will  be  necessarily  slow. 

Kaolin,  apparently  derived  from  the  weathering  of  a  granite  vein, 
has  been  reported  from  the  vicinity  of  Custer,  but  much  of  it  is  said  to 
be  white-burning  and  of  comparatively  easy  fusibility.  The  possibility 
of  finding  it  in  the  Harvey  Peak  and  Nigger  Hill  regions  is  also  sug- 
gested. 

Fire-clays  are  found  at  three  or  four  horizons  in  the  Fuson  formation 
of  the  Cretaceous,  and  are  best  developed  in  the  vicinity  of  Rapid  City, 
where  they  have  been  used  for  fire-brick  manufacture.  Similar  beds 
occur  at  Hot  Springs.  Analyses  of  the  Rapid  City  clays  are  given  below. 

It  is  possible  that  fire-clays  may  underlie  the  lignite  beds  of  the 
La  ramie  in  the  Cave  Hills,  but  no  search  has  been  made  for  them. 

Potter's  clays  have  not  been  definitely  located,  but  there  are  many 
drab  and  gray  plastic  shales  in  the  Fuson,  Dakota,  Pierre,  and  Laramie 
formations  of  the  Cretaceous,  which  might  answer  for  this  purpose. 
Some  of  the  Tertiary  beds  may  also  prove  of  value. 

These  materials  are  distributed  in  all  parts  of  the  State,  but  east 
of  the  Missouri  River  the  heavy  covering  of  glacial  deposits  renders 
them  more  or  less  inaccessible,  except  where  they  have  been  exposed 
along  the  larger  streams. 

Brick-clays  have  not  been  extensively  worked.  Professor  Todd  states 
that:  "Over  much  of  the  State,  particularly  in  close  proximity  to  the 
principal  towns,  good  brick-clay  is  not  very  accessible.  This  results 
from  the  fact  that  the  settlements  have  been  mainly  made  in  the  glacial 
region  east  of  the  Missouri  and  in  the  mountainous  region  of  the  Black 

1  S.  Dak.  Geol.  Surv.,  Bull.  No.  3,  pp.  101-107,  1902. 


420  CLAYS 

Hills,  where  the  clays  are  generally  stony.  ...  In  the  regions  between, 
where  clay  is  more  abundant,  the  population  has  been  small  and  fuel 
scarce." 

Alluvium  is  used  for  common  and  pressed  brick  at  Vermilion,  Clay 
County,  and  the  same  products  are  made  from  similar  materials  at 
Rapid  City,  De  Smet,  Big  Stone  City,  Lead  City,  etc. 

The  glacial  clays  are  usually  unsatisfactory,  because  of  the  pebbles 
and  concretions  which  they  contain. 

ANALYSES  OF  SOUTH  DAKOTA  CLAYS 

I.  II.  III. 

Silica  (SiO2) '. 83.30  76.78  81.98 

Alumina  (A12O3) 12.30  14.43  13.08 

Ferric  oxide  (Fe2O3) 0.80  0.18  0.21 

Lime  (CaO) 1.30  2.18  1.46 

Magnesia  (MgO) trace  0.95  0.31 

Alkalies  (Na2O,K*°) trace  trace 

Loss  on  ignition 4 . 62  4 . 07 

97.70  99.14  101.11 

I.  Rapid  City. 

II    East  slope  of  ridge  at  Rapid  City    \  From  S.  Dak.  Geol.  Surv.,  Bull   3. 
III.  Rockerville  Hill,  Rapid  City. 

References  on  South  Dakota  Clays 

1.  Todd,  J.  E.,The  Clay  and  Stone  Resources  of  South  Dakota,  Eng. 
and  Min.  Jour.,  LXVI,  p.  371,  1898. 

2.  Todd,  J.  E.,  The  Mineral  Resources  of  South  Dakota,  S.  Dak. 
Geol.  Surv.,  Bull.  3. 

Tenneesse 

Probably  less  is  known  regarding  the  clays  of  Tennessee  than  those 
of  any  other  Eastern  States.  The  geologic  formations  occurring  in  Tenn- 
essee include  pre-Cambrian,  Cambrian,  Ordovician,  Silurian,  Devonian, 
Carboniferous,  Eocene,  and  Pleistocene. 

The  pre-Cambrian  rocks  occur  in  small  areas  along  the  eastern  border, 
while  west  of  them,  and  folded  into  many  narrow  belts,  lie  rocks  of  Cam- 
bro-Silurian  age.  The  Carboniferous  extends  from  the  eastern  edge  of 
the  Cumberland  Plateau  westward  to  beyond  the  Tennessee  River.  A 
large  area  of  Silurian  is  found  in  the  central  part  of  the  State,  while 
another  is  found  along  the  Tennessee  River  in  the  southern  half  of  the 
State.  This  is  followed  by  a  broad  belt  of  Tertiary,  which  in  turn  is 
separated  from  the  Mississippi  River  by  a  band  of  Pleistocene. 


NORTH   DAKOTA  TO  WYOMING  421 

Pre-Cambrian  Clays 

No  kaolin-deposits  have  been  described  from  the  crystalline  area, 
of  eastern  Tennessee,  although  it  is  probable  that  some  at  least  exist,  as 
the  author  has  seen  samples  of  kaolin  from  this  region.  They  will  be  of 
little  commercial  value,  however,  unless  located  fairly  close  to  lines  of 
transportation. 

Palaeozoic  Residual  Clays 

The  rocks  of  the  Palaeozoic  formations  yield  residual  clays  from 
both  limestones  and  shales.  These  are  usually  impure,  although  often 
tough  and  plastic,  and  are  much  used  for  brick-  and  tile-making.1 

Some  of  the  highly  siliceous  clays  derived  from  the  Knox  dolomite- 
are  refractory,2  and  fire-brick  are  made  from  them  near  Cleveland.  At 
Smith ville  a  white  clay,  derived  from  the  slate  in  the  upper  part  of  the 
Fort  Payne  division,  is  used  for  pottery. 

Carboniferous 

There  is  but  little  recent  reliable  information  relating  to  Carbon- 
iferous clays  or  shales  in  Tennessee. 

J.  M.  Safford,  in  his  report  on  the  Geology  of  Tennessee  published 
in  1869,  refers  to  the  following  occurrences  of  clay  in  the  Carboniferous: 

Near  the  Cumberland  Iron  Works,  in  Stewart  County,  is  a  bed  of 
fire-clay  of  Lower  Carboniferous  age;3  another  occurs  4  miles  southwest 
of  Cumberland  City,  in  Stewart  County;  in  the  valley  of  Crow  Creek, 
near  Anderson  station,  the  coal-measures  at  the  margin  of  the  table- 
land show  a  fire-clay  3  feet  thick,  163  feet  below  the  top  of  the  cliff;4  in 
Franklin  County,  near  the  Grundy  County  line,  and  4  miles  northwest 
of  the  track  of  Sewanee  road  at  the  old  Logan  bank,  is  a  bed  of  clay  115 
feet  below  the  conglomerate;  5  near  the  lower  end  of  the  Battle  Creek 
Valley,  in  Marion  County,  is  a  bed  of  fire-clay  2  feet  thick;  5  miles  south- 
east of  Tracy  City,  and  1 J  miles  from  Parmly  Bank,  a  bed  of  clay  under- 
lies the  main  Sewanee  coal;  6  another  occurs  at  the  north  end  of  Lookout 

1  Many  scattered  references,  but  of  very  brief  character,  are  to  be  found  in  the 
U.  S.  Geol.  Surv.,  Geol.  Atlas  Folios,  as  follows:  No.  21  (Pikeville);  16  (Knoxville); 
59  (Bristol);    4  (Kingston);    8  (Sewanee);    2  (Ringgold);    53  (Standingstone);  40 
Wartburg;  27  (Morristown);  22  (McMinn ville). 

2  U.  S.  Geol.  Surv.,  Geol.  Atlas,  Folio  No.  2  (Ringgold). 

3  Safford,  Geology  of  Tennessee,  p.  349. 

4  Ibid.,  p.  372. 

5  Ibid.,  p.  373. 
8  Ibid.,  p.  380. 


422  CLAYS 

Mountain,  below  the  upper  conglomerate.1  Many  of  the  under-clays  of 
the  coal-seams,  according  to  Safford,  are  of  refractory  character.2  Fire- 
clays, mostly  undeveloped,  are  said  to  be  associated  with  the  coals  in 
the  areas  covered  by  the  following  Geologic  Atlas  Folios:  Standingstone, 
No.  53;  Wartburg,  No.  40  (used  for  pottery).3 

In  the  Kingston  region  the  beds  of  clay  which  underlie  the  coals  are 
no  doubt  refractory  in  many  cases,  but  they  are  wholly  undeveloped.4 

Tertiary 

In  western  Tennessee  the  plastic  clay  immediately  underlying  the 
Lafayette  formation  serves  as  the  basis  of  a  rather  active  stoneware 
and  fire-brick  industry.  The  section  usually  seen  in  the  clay-pits  involves 
red  Lafayette  sands,  which  seem  to  overlie  unconformably  the  beds  of 
stoneware-clay  and  white  sands. 

One  pottery,  located  at  Grand  Junction,  used  clay  from  the  various 
pits  of  the  vicinity.  The  clay  varies  in  quality.  In  the  pits  of  the 
Irwin  Clay  and  Sand  Company,  1J  miles  east  of  the  station,  along  the 
railroad,  the  section  is : 5 

Feet.        Inches. 
Red  Sand 

White  sand 8 

White  clay 8 

Gray  lignitic  clay 8  10 

White  clay 20 

The  clay-deposits  are  very  irregular,  sometimes  running  together  to 
form  overlapping  lenses  in  the  white  and  yellow  sand.  Potteries  are  in 
operation  at  Mackenzie,  Jackson,  and  Pinson,  but  at  the  latter  locality 
the  clay  is  also  used  for  fire-brick  and  tiles.6 

The  clay  at  Hico,  3  miles  south  of  Mackenzie,  is  shipped  to  the  pot- 
teries at  Akron  and  East  Liverpool,  Ohio,  and  Louisville,  Ky.,  while 
the  clays  from  Hollow  Rock  are  shipped  to  Nashville. 

1  Safford,  Geology  of  Tennessee,  p.  385. 

2  Ibid.,  p.  513. 

3  See  also  Geologic  Atlas  U.  S.  Folio  33,  Briceville;  Folio  21,  Pikeville;  Folio  4 
Kingston. 

4  Idem,  Folio  4,  Kingston. 

6  Eckel,  U.  S.  Geol.  Surv.,  Bull.  213,  1903,  p.  382. 
8  Idem. 


NORTH   DAKOTA  TO  WYOMING  423 

Three  miles  east  of  Currier  are  the  pits  of  I.  Mandle,  where  an  area 
60  by  50  feet  has  been  opened  up.  The  section  is  as  follows: 

East  Side.  West  Side. 

2  feet  clay Reddish  sand 

4  feet  clay 15  feet  light-gray  clay 

1  foot  black  clay  (lignitic) 1  foot  black  clay 

5  feet  brown  clay  (ball-clay) 5  feet  ball-clay 

The  bases  of  the  two  sections  are  at  the  same  level,  hence  the  beds 
are  very  irregular.  The  light-gray  clay  is  shipped  to  East  Liverpool, 
Ohio,  for  saggers,  and  the  ball-clay  is  known  as  Tennesssee  ball-clay 
No.  3.  Tests  of  samples  of  this  clay,  made  by  S.  Geijsbeek,  show  that 
it  leaves  10  per  cent  residue  on  a  175-mesh  sieve.  Its  rational  com- 
position is: 

Per  cent. 

Clay  substance 91 . 35 

Feldspar 2.70 

Quartz 5 . 95 

It  will  carry  as  much  as  72  per  cent  of  non-plastic  material.  Tha 
shrinkage  at  cone  1  is  12.5  per  cent;  at  cone  2,  18  per  cent.  It  burns- 
white  at  cone  1  and  gray  at  cone  8,  being  vitrified  at  that  temperature. 
This  is  located  5  miles  from  Paris,  and  the  clay  is  shipped  from  Currier,, 
which  is  3  miles  from  the  mine. 

Tennessee  ball-clay,  No.  1,  found  in  Henry  County,  shows  the  follow- 
ing rational  analysis: 

Per  cent. 

Clay  substance 86 . 20 

Feldspar 2.70 

Quartz 11.10 

It  carries  60  per  cent  non-plastic  material  to  the  mixture.  The 
total  fire-shrinkage  at  cone  8  is  15  per  cent,  and  at  this  temperature 
it  burns  to  a  cream-white  color  and  dense  body. 

Alluvial  Clays 

Alluvial  clays  are  found  in  many  of  the  river  valleys,  and  in  most 
cases  are  the  wash  from  the  residual  clays  of  surrounding  areas.  They 
often  underlie  the  river  terraces.  These  terrace-clays  are  used  in  the 
Maynardville  area.1  Others  are  common  in  the  region  around  Morris- 

1  See  Geologic  Atlas  U.  S.  Folio  75,  Maynardville. 


424 


CLAYS 


iown,1  especially  in  the  low  grounds  of  the  Lick  Creek,  Nolichucky,  and 
French  Broad  valleys. 

The  following  analyses  of  Tennessee  clays  have  been  gathered  from 
different  sources; 

ANALYSES  OF  TENNESSEE  CLAYS 


Locality. 

Si02. 

A1203. 

Fe203. 

CaO. 

MgO. 

Alk. 

H2O. 

Mois- 
ture. 

MnO. 

Remarks. 

45  06 

30  03 

4  50 

4  70 

4  80 

10 

1 

Crossley,  analyses  of 

Powdes  Station. 

68  35 

12.96 

6.44 

0.23 

1 

2  14 

7 

8 

0.9 

clays 
J.  W.  Slocum,  anal 

Chattanooga.  .  . 

68  96 

20.42 

1.84 

0.16 

0.33 

2.18 

6.50 

trace 

Tennessee     Paving- 

brick  Co. 

Hobbins  

70.57115.19 

7.97 

0.78 

0.32 

2.80 



Clay-worker,     Dec., 

1 

1893 

References  on  Tennessee  Clays 

1.  Eckel,  E.  C.,  Stoneware  and  Brick-clays  of  Western  Tennessee 
and  Northwestern  Mississippi,  U.  S.  Geol.  Surv.,  Bull.  213,  p.  382,  1903. 

2.  Ries,  H.,  The  Clays  of  the  United  States  East  of  the  Mississippi 
Hiver,  U.  S.  Geol.  Surv.,  Prof.  Pap.  11,  1903. 

Texas 

Deposits  of  clay  or  shale  are  scattered  over  all  parts  of  Texas,  but 
only  those  in  the  eastern  part  of  the  State  have  been  systematically 
investigated.  Indeed,  it  is  not  likely  that  those  occurring  in  the  western 
part  will  be  developed  to  any  extent  for  some  time,  owing  to  the  sparsely 
settled  character  of  the  country  and  lack  of  transportation. 

The  annual  reports  of  the  First  Geological  Survey  contain  scattered 
references  to  clay-deposits,  but  few  tests.  In  1903  the  University 
Mineral  Survey  undertook  an  examination  of  those  deposits  lying  east 
of  the  99th  meridian,  and  the  results  of  this  work  have  appeared  in 
condensed  form.2  The  following  remarks,  unless  otherwise  stated,  deal 
with  the  area  mentioned. 

The  map,  Fig.  63,  shows  the  location  of  nearly  all  the  deposits  examined, 
their  relation  to  the  geology  of  the  State,  and  the  type  of  clay  found  at 
each  locality.  From  this  map  it  will  be  seen  that  the  clay-deposits 
found  within  the  area  under  discussion  range  from  Carboniferous  to 
Pleistocene  in  age,  the  older  deposits  being  found  in  the  northwestern 


1  Geologic  Atlas  U.  S.,  Folio  27,  Morristown. 

2  Amer.  Inst.  Min.  Eng.,  Bimon.  Bull.,  1906. 


NORTH  DAKOTA  TO  WYOMING 


425 


part  of  the  area,  while  those  of  the  Cretaceous  and  Tertiary  lie.  to  the 
east,  southeast,  and  south.     The  Pleistocene  clays  are  found  in  part  in 


LEGEND 


?J 


LOWER  CRETACEOUS 


EXPLANATION  OF  CLAY  SYMBOLS 


•  +  • 

SLIP  CLAY      FIRECLAY    STONEWARE 


COAL  MEASURES 


X                            O                           A  A 

RED  AND  BROWN  CALCAREOUS      SANDY  PAVIN6  BRICK        fcj^VSSj 

APPROXIMATE  SCALE  PRE-CARBONIFEROuS 

0           30            60           90  120  MILES 


FTG.  63. — Map  of  eastern  Texas,  showing  distribution  of  clay-bearing  formations. 
(Compiled  from  various  survey  reports.) 

a  belt  along  the  coast,  and  in  part  along  many  of  the  larger  rivers,  where 
they  often  underlie  extensive  terraces. 


426  CLAYS 

Carboniferous  Clays 

The  Carboniferous  rocks  of  northern  Texas  outcrop  in  a  broad  belt 
extending  from  the  south  side  of  the  Colorado  River  Valley,  between 
Lampasas  and  Concho  counties,  northward  as  far  as  the  Red  River 
in  Montague  County.  This  belt  is  about  250  miles  long  and  averages 
about  45  miles  in  width.  The  rocks  consist  of  a  succession  of  shales  and 
sandstones,  together  with  occasional  beds  of  limestone  and  coal,  showing 
a  gentle  west  and  northwest  dip  of  a  few  feet  per  mile.  The  entire  series 
is  subdivided  into  five  groups  (Ref.  2).  Scattered  through  these  are  a 
number  of  beds  of  shale  of  excellent  quality,  some  of  which  are  asso- 
ciated with  the  coal-seams  and  could  be  mined  in  connection  with 
them,  while  others  outcrop  on  the  surface  (PI.  XXXVII,  Fig.  1),  where 
they  are  easily  accessible  for  working. 

These  shales  have  been  worked  at  only  three  localities,  namely,  Tlmr- 
ber,  Millsap,  and  Weatherf  ord,  and  are  used  for  dry-pressed  brick,  stiff-mud 
paving-brick,  and  for  pottery.  Other  good  deposits  are  known  to  occur 
at  Graham,  Bridgeport,  and  Cisco.  None  of  these,  as  far  as  known,  are 
of  refractory  character.  Some,  as  might  be  expected  from  their  close 
association  with  coal-seams,  are  quite  carbonaceous,  and  therefore 
of  less  value,  because  of  the  trouble  they  would  cause  in  burning.  The 
uniformity  of  the  Carboniferous  shale-beds  is  much  greater  than  that 
of  the  Tertiary  clays,  and  they  moreover  extend  over  greater  areas. 

Cretaceous  Clays 

Lower  Cretaceous. — The  formations  of  this  age  occupy  an  area  to 
the  east  and  south  of  the  Carboniferous  beds.  They  are  not  utilized,  nor 
do  they  appear  to  contain  any  deposits  of  use  for  anything  better  than 
common  brick.  They  can  therefore  be  passed  over.  Near  Leaky, 
Edwards  County,  Texas,  there  occur  some  most  curious  deposits  of  a 
white  clay,  which  has  usually  been  referred  to  as  kaolin.1  The  material 
is  a  whitish  clay,  with  pink  and  purplish  mottlings,  which  forms  vein- 
like  deposits  in  the  Edwards  limestone.  Scattered  through  it  are  crys- 
talline masses  of  aragonite(?).  Owing  to  the  condition  of  the  workings 
it  is  difficult  to  determine  its  exact  relations  to  the  surrounding  limestone. 
As  the  deposits  are  of  small  extent  and  40  miles  from  the  railroad  their 
commercial  value  is  doubtful. 

Upper  Cretaceous. — This  division  of  the  Cretaceous  carries  a  number 
of  important  clay-deposits,  some  of  which  are  of  great  extent,  but 
unfortunately  are  not  the  most  valuable  clay-beds  in  the  State. 

1  First  Geol.  Surv.  of  Texas,  2d  Ann.  Kept,,  p.  li,  1891. 


NORTH  DAKOTA  TO  WYOMING  427 

The  Upper  Cretaceous  rocks  extend  across  Texas  in  a  broad  belt 
from  the  Red  River  north  of  Sherman  down  to  Eagle  Pass,  which  lies  about 
the  middle  of  the  band.  Fort  Worth  is  on  the  western  edge  and  Austin 
towards  the  southeastern  border.  A  second  belt  extends  along  the  Red 
River,  with  narrowing  width,  until  it  passes  out  of  the  State  in  the 
northeastern  corner.  Since  the  dip  is  to  the  southeast,  the  older  beds 
are  found  along  the  western  edge  of  the  belt,  and  the  higher  or  younger 
ones  on  the  east  where  they  pass  below -the  Tertiary  strata.  Owing  to 
the  dissimilarity  of  the  several  numbers  of  this  group,  it  becomes  neces- 
sary to  refer  to  them  individually,  beginning  with  the  oldest. 

Woodbine  formation. — This  consists  of  a  series  of  sandstones,  clays, 
and  clayey  sands,  often  containing  leaf  impressions  and  lignite.  While 
the  clay -beds  are  usually  sandy  or  even  bituminous,  they  become  locally 
pure  enough,  as  at  Denton,  to  be  utilized  for  clay-products,  although 
even  here  the  beds  are  rarely  of  great  extent  and  usually  interbedded 
with  sands.  The  clays,  which  are  worked  at  both  Denton  and  Lloyd, 
closely  resemble  the  stoneware-clays  of  the  Tertiary  beds  to  the 
southeast.  They  are  mostly  of  very  plastic,  semi-refractory,  buff- 
burning  character  and  are  utilized  for  both  common  stoneware  and 
pressed  brick. 

Eagle  Ford  formation. — This  includes  a  series  of  bituminous  clay- 
shales,  which  in  places  contain  thin  limestone  beds.  It  is  one  of  the 
most  extensive  and  thickest  clay-bearing  formations  in  the  entire  State 
of  Texas,  and  occupies  a  rather  long  narrow  belt,  as  shown  in  Fig.  63. 
While  the  Eagle  Ford  clay  is  of  great  thickness  and  well  located  for 
working,  it  contains  about  all  the  undesirable  elements  that  a  clay  might 
have,  namely,  concretions,  limestone  pebbles,  gypsum  lumps,  and  even 
pyrite.  Moreover,  its  bituminous  character,  as  well  as  extreme  tough- 
ness, causes  great  trouble  in  its  manipulation,  and  practically  forces  the 
clay-worker  to  mold  it  by  one  method,  the  dry-press  process,  other  means 
yielding  a  brick  of  too  dense  character  to  permit  the  carbon  in  the  clay 
to  burn  off.  The  clay  is  red-burning,  and  extensively  used  for  bricks 
around  Paris,  Sherman,  Dallas,  and  Waco. 

Taylor-Navarro  marls,  overlying  the  Eagle  Ford  stratigraphically  but 
separated  from  it  by  the  Austin  Chalk,  form  an  extensive  belt  of  clay, 
which  parallels  that  of  the  Eagle  Ford  formation.  The  beds  are  marly 
clays,  and  in  their  general  physical  and  chemical  properties  bear  a  close 
resemblance  to  the  Eagle  Ford  beds.  The  Taylor  marls  are  not  clearly 
distinguishable  from  the  Navarro  marls,  which  outcrop  to  the  southeast 
of  them  and  resemble  them  closely,  and  for  this  reason  the  two  are 
included  under  a  single  head. 


428  CLAYS 

The  Taylor-Navarro  marls  are  all  plastic,  sometimes  glauconitic, 
red-burning  clays,  and  are  worked  for  dry-press  brick  at  Cooper,  Green- 
ville, Corsicana,  Taylor,  and  Ferris. 

At  Eagle  Pass,  which  lies  outside  the  east  and  central  Texas  area 
studied,  the  Eagle  Pass  formation,  which  occurs  at  the  top  of  the  Upper 
Cretaceous,  contains  shales  associated  with  the  coals,  and  while  some 
of  these  at  least  are  probably  adapted  to  the  manufacture  of  clay-products, 
no  tests  of  them  are  available. 


Tertiary  Clays 

The  clays  found  in  the  Tertiary  formations  include  the  most  import- 
ant ones  in  eastern  Texas,  but,  owing  to  the  lenticular  character  of  the 
beds  and  the  enveloping  deposits  of  sand  with  which  they  are  frequently 
associated,  prospecting  for  them  is  often  rendered  more  or  less  difficult. 
From  the  wide  distribution  of  the  deposits  (Fig.  63)  it  would  appear 
that  in  certain  belts  of  the  Territory  at  least,  as  mentioned  below,  clays 
are  to  be  sought  for  with  excellent  chances  of  success. 

In  Webb  County,  west  of  Laredo  in  southern  Texas,  shales  are  found 
associated  with  the  Eocene  coals,  and  some  of  those  obtained  from  the 
mines  at  Cannel  are  weathered  and  then  shipped  to  Laredo  for  making 
dry-pressed  brick. 

The  other  Tertiary  beds  of  eastern  Texas  consist  largely  of  uncon- 
solidated  materials  which  range  from  coarse  gravels  to  very  fine  clay, 
but  containing  occasional  beds  of  sandstone,  limestone,  and  lignite. 
Several  members  are  recognized,  namely,  Will's  Point,  Lignitic,  Marine, 
Yegua,  Fayette,  and  Frio.  Of  these  only  the  Lignitic  and  Marine  are 
of  importance. 

Lignitic. — These  beds  outcrop  in  a  long  but  irregular  belt  (Fig.  63), 
and  contain  the  following  types: 

1.  Beds   of   plastic,    buff-burning,    semi-refractory    clay    associated 
with  the  lignite  deposits;  they  are  well  adapted  to  the  manufacture  of 
pressed  brick. 

2.  Red-burning,   plastic,   gritty   clays,   overlying   the    lignites,   and 
worked  at  Rockdale  for  dry-pressed  brick. 

3.  Red-burning,  tough,  shaly  clay,  occurring  at  New  Boston  and 
Sulphur  Springs. 

4.  A  widely  distributed  series  of  grayish,   highly  plastic   clays  of 
refractory  or  semi-refractory  character,  and  used  for  stoneware,  fire- 
brick, etc.     The  following  analyses  p.  (431)  represent  groups  I,  II,  III. 


PLATE  XXXVIII 


F:G.  1. — Bank  of  sewer-pipe  clay  in  Lignitic  (Tertiary)  formation,  Saspamco,  Texas. 
Shows  electric  system  of  haulage.     (Photo  by  H.  Ries.) 


FIG.  2. — Pit  in  Beaumont  clay,  Houston,  Tex.     The  walls  of  the  pit  are  a  very 
sandy  clay  underlying  the  other.     (Photo  by  H.  Ries.) 

429 


NORTH  DAKOTA  TO  WYOMING  431 

ANALYSES  OF  TERTIARY  CLAY  TYPES 

I-  II.  III. 

Silica  (SiO2) 69.33  72.99  70.65 

Alumina  (A12O3) 19.38  14.70  18.14 

Ferric  oxide  (Fe2O8) 1 . 06  4.5  0 . 82 

Lime  (CaO) 0.86  0.6  0.339 

Magnesia  (MgO) 0.86  0.3  0.628 

Potash  (K2O) trace  1.5  0.41 

Soda  (Na2O) 0.08  0.7  0.55 

Titanic  acid  (TiO2) 1.40  1.00  1.14 

Water  (H2O) 5.49  4.20  6.18 

Stoneware  is  made  from  these  clays  at  Elmendorff,  Athens,  etc.; 
fire-bricks  at  Athens  and  Sulphur  Springs;  sewer-pipe  at  Saspamco,  and 
pressed  brick  at  Elgin,  Athens,  Malakoff,  etc. 

Marine  beds. — These  are  usually  of  sandy  or  glauconitic  character, 
but  here  and  there  carry  clay-deposits  of  some  economic  value,  and 
adapted  to  making  buff  brick  and  stoneware.  They  are  worked  at 
Nacogdoches,  Henderson,  and  Rusk. 

Pleistocene 

This  formation  includes  clays  of  several  types.  They  form  a  rather 
broad  belt  along  the  Gulf  Coast  (Fig.  63),  where  they  are  mostly  of 
sandy  character, .  the  Beaumont  clays  worked  for  brick  around  Beau- 
mont and  Houston  being  the  most  notable  exception.  These  are  tough, 
plastic,  brown,  blue,  and  yellow  clays,  carrying  irregularly  distributed 
nodules  of  limestone  and  underlying  a  broken  belt  extending  from  Cal- 
houn  County  to  Jefferson  County.  They  are  all  red-burning,  and  used 
chiefly  for  common  brick  and  to  a  lesser  extent  for  dry-press  brick. 

A  second  important  type  includes  the  river  silts  found  underlying 
the  terraces  along  many  of  the  large  rivers,  such  as  the  Rio  Grande, 
Colorado,  Neches,  etc.  These  clays  are  always  silty  or  sandy  and  highly 
calcareous,  the  lime  carbonate  being  present  as  concretions,  lumps,  shells, 
or  in  a  finely  divided  condition,  and  forming  at  times  over  50  per  cent  of 
the  material  without  apparently  diminishing  its  plasticity.  They  are 
especially  well  seen  and  extensively  worked  at  Austin  and  Laredo. 
Though  chiefly  used  for  common  brick,  these  clays  have  also  been  worked 
for  pressed  brick,  and  in  a  few  localities,  as  near  San  Antonio,  they 
are  of  the  proper  character  for  employment  as  a  slip  for  stoneware.  For 
practical  purposes  the  clays  found  within  the  area  just  discussed  can 
be  divided  into  the  following  groups:  I.  Fire-clays;  II.  Stoneware- 
clays;  HI.  Brick-clays;  (a)  Buff-burning,  non-calcareous;  (6)  Red  and 
brown-burning;  (c)  Calcareous;  (d)  Sandy;  IV.  Paving-brick  clays; 


432 


CLAYS 


V.  Slip-clays.     Their  distribution  is  shown  on  the  map  Fig.  63  and  a 
few  representative  analyses  are  given  below. 

ANALYSES  OF  TEXAS  CLAYS 


I. 

II. 

III. 

IV. 

V. 

VI. 

VII. 

VIII. 

Silica  (SiO2)  

63  07 

63.43 

45  44 

55.10 

49.45 

73  00 

72  9 

64  84 

Alumina  (Al2Oa)  

19.43 

23.42 

40.30 

23.80 

17.11 

15.79 

14.7 

22  44 

Ferric  oxide  (Fe2O3).  .  .  . 
Lime  (CaO)  
Magnesia  (MgO)  
Potash  (K2O)  
Soda  (Na2O)  
Titanic  acid  (TiO2).  .  .   . 
Water  (H2O) 

4.75 
1.32 
0.50 

1.47 
6  90 

1.15 
0.45 
1,23 
0.07 
0.26 
1.13 
7  00 

0.54 
trace 
trace 
trace 
0.38 
trace 
13  29 

3.51 
3.28 
1.24 
0.50 
0.21 
1.05 
6  00 

3.45 
12.67 
1.77 
0.13 
0.21 
0.70 
4  84 

0.63 
1.29 
1.53 
0.10 
0.16 
0.43 
5  76 

4.5 
0.6 
0.3 
1.5 
0.7 
1.0 
4  2 

0.80 
trace 
0.74 
0.12 
0.71 
1.40 
6  42 

Sulphur  trioxide  (SO3).. 
Organic  matter 

0.15 

0  40 

3.37 

2.00 

Carbon  dioxide  (CC>2) 

1.75 

7.10 

Total 

99  09 

100.54 

99.95 

99.81 

99.43 

98.69 

99.5 

99  47 

IX. 

X. 

XI. 

XII. 

XIII. 

XIV. 

XV. 

Silica  (SiO2) 

74  04 

66  01 

57  01 

77  75 

49  40 

90  00 

53  6 

Alumina  (Al2Os)     . 

15  15 

18  82 

11  85 

11  04 

17  90 

4  60 

9  0 

Ferric  oxide  (Fe2Os). 

0  50 

6  33 

3  02 

3  K 

4  50 

1  44 

2  6 

Lime  (CaO) 

0  50 

0  55 

9  56 

0  84 

9  50 

0  10 

17  8 

Magnesia  (MgO)  

0  27 

1  88 

1  20 

0.38 

1.8S 

0  10 

1  2 

Potash  (K2O)  

0  42 

0  16 

0.75 

trace 

1  8 

Soda  (Na2O)             

1   12 

0  08 

2  01 

trace 

trace 

trace 

Titanic  acid  (TiO2)  

1.31 

0  95 

1  13 

1.23 

1  05 

0  70 

8 

Water  (H2O)  

6  00 

4  80 

4  00 

3.24 

4.58 

3  04 

1 

Sulphur  trioxide  (SOs).  . 

0.51 

Organic  matter  

Carbon  dioxide  (CO2).  .  . 





8.00 

9.55 



11.6 

Total  

99.31 

99.58 

98.53 

98.40 

97.36 

99  98 

99  40 

PHYSICAL  TESTS  OF  TEXAS  CLAYS 


I. 

II. 

III. 

VI. 

VIII. 

IX. 

Per  cent 
Plasticity 
Average 
Air-shrin 

Cone  05  - 
Cone    1 
Cone    5 

Cone    9 

Cone  of  f 
Color  aft 

water  required.  . 

25.3 
good 
333 
7.7 
5.6 
3.58 
6.3 
0.10 

23.1 
good 
202 
9.6 
5 
2.02 

44 
low 
159 
6.2 
5 
32.  7f 
10 
20.47 
13.7 
10  7 

33 

high 
487 
12.4 
4* 

'4*' 

33 
high 
304 
9.3 

1 
12.9 

2.7 
7.87 
3.5 
3.15 

30.8 
high 
257 
10.2 
1.6 
11.44 
3.3 
6.57 
5.7 
2.83 
9.4 
0.82 
28 
buff 

r 

-ensile  strength,  Ibs.per.  sq.in. 
sage,  per  cent  

f  Fire-shrinkage,  per  cent.  .  .  . 
Absorption  per  cent 

'  Fire-shrinkage,  per  cent.  .  .  . 
Absorption,  per  cent  
Fire-shrinkage  per  cent. 

Absorption   per  cent 

Fire-shrinkage  per  cent.  .  . 

vit'd 

14.7 
8  6 

Absorption,  per  cent  

usion  

5 
red 

14 
buff 

35 

white 

5 
red 

12 
red 

er  burning  

*Dry  Pressed. 


NORTH  DAKOTA  TO  WYOMING 


433 


PHYSICAL  TEST.S  OF  TEXAS  CLAYS — Continued 


X. 

XI. 

XII. 

XIII. 

XIV. 

XV. 

Per  cent  water  reumred 

23.1 
good 
155 
8.5 
0 
15.68 
1.6 
13.13 
3 
14.05 
4.3 
6.83 
30 
buff 

37.4 
high 
154 
11.6 
5.33* 
16.49 
11.33* 
5.77 

23.1 
good 
303 
9.4 
0.3 
10.52 
0.3 
9.39 
0.4 
7.29 

23 
high 
316 
9.3 
0.4 
6.63 
0.8 
4.43 

5 
red 

25.4 
low 
77 
4 
-0.3 
9.14 
0 
9.45 
0.7 
9.55 
1.3 
8.39 
12 
red 

25.3 

good 
253 
6.2 
-4.7 

i 

23.49 
7 
5.95 

Plasticity 

Average  tensile  strength,  Ibs.  per  sq.  in. 
Air  shrinkage   per  cent 

fYmP  n^  J  Fire-shrinkage,  per  cent.  .  . 
*°  \  Absorption,  per  cent  
p           1  |  Fire  -shrinkage,  per  cent.  .  .  . 
\  Absorption,  per  cent  
fi           r  /  Fire-shrinkage,  per  cent.  .  .  . 
\  Absorption,  per  cent  
P          Q  j  Fire-shrinkage,  per  cent.  .  .  . 
1  Absorption,  per  cent  
Cone  of  fusion  
Color  after  burning  

5 
red 

V 

red 

7 
cream 

*  Dry  pressed. 


LOCALITIES  OF  PRECEDING  ANALYSES 


No. 

Location. 

Age. 

Use. 

1 

1  hurber  Erath  County 

Coal-measures.  . 

Paving-brick 

II. 

Top   clay  over   lower  coal,  Minera, 
Webb  County  

Cretaceous.  . 

Un  worked 

Ill 

L°aky,  Edwards  County  

i  ( 

i  ( 

IV 

Dallas  Dallas  County  

Eagle-  Ford-Creta- 

ceous. .  . 

Brick 

V. 
VI. 
VII. 
VIII. 
IX. 
X. 
XI. 

Ferris,  Ellis  County  
S.  E.  of  Lena,  Fayette  County  
Vogel  mine,  Rockdale,  Milan  County. 
Saspamco,  Bexar  County  
Athens,  Henderson  County  
New  Boston,  Bowie  County  .*. 
Alazan  Creek,  San  Antonio,  Bexar 
County 

Taylor  marls  
Tertiary  

Lignitic-Tertiary 

n             n 

t  (             (( 
Tertiary  '.'. 

Pleistocene 

(  t 

Un  worked 
Brick 
Sewer-pipe 
Fire-brick 
Pressed  brick 

Slip-clay 

XII 

Beaumont  Jefferson  County 

t  < 

Pressed  brick 

XIII 

Houston  Harris  County 

i  * 

(  t 

XIV. 

XV 

Colmesneil,  Tyler  County  
Austin  Travis  County.  .  . 

(  t 
1  '         '  ter- 

Common  brick 

race-clay 

Common  brick 

Nos.  VII  and  XV,  S.  H.  Wcrrell.  analyst;  the  rest  analyzed  by  O.  H.  Palm. 

References  on  Texas  Clays 

1.  Adams,  G.  I.,  Oil-  and  Gas-fields  of    the  Western  Interior  and 
Northern  Texas  Coal-measures,  U.  S.  Geol.  Surv.,  Bull.  184,  pp.  37  to 
47,  1901. 

2.  Drake,  N.  F.,  and  Thompson,  R.  A.,  The  Colorado  Coal-field  of 
Texas,  4th  Ann.  Kept.,  Tex.  Geol.  Surv.,  p.  357,  1893. 

3.  Hayes,  C.  W.,  and  Kennedy,  W.,  Oil-fields  of  the  Texas  Louisiana 
Gulf  Coastal  Plain,  U.  S.  Geol.  Surv.,  Bull.  212,  pp.  15  to  32,  1903. 


434  CLAYS 

4.  Hill,  R.  T.,  Geology  and  Geography  of  Black  and  Grand  Prairies, 
U.  S.  Geol.  Surv.,  21st  Ann.  Kept.,  Pt.  VII,  p.  295,  1.901. 

5.  Kennedy,  Wm.,  Texas  Clays  and  Their  Origin,  Science,  XXII,  p. 
297,  1893. 

6.  Penrose,  R.  A.  F.,  Preliminary  Report  on  the  Geology  of  the 
Gulf-Tertiary  of  Texas,  Tex.  Geol.  Surv.,  1st  Ann.  Kept.,  p.  5,  1890. 

7.  Ries,  H.,  The  Clays  of  Eastern  Texas,  Trans.  Amer.  Inst.  Min. 
Eng.,  Bimonthly  BulL,  1906. 

8.  Taff,  J.  A.,  and  Leverett,  S.,  The  Cretaceous  Area  North  of  the 
Colorado  River,  Tex.  Geol.  Surv.,  4th  Ann.  Kept.,  p.  241,  1893. 

9.  Vaughan,  T.   W.,  Reconnaissance  in  the  Rio  Grande  Coal-fields 
of  Texas,  U.  S.  Geol.  Surv.,  BulL  164,  1900. 

10.  See  also  scattered  references  in  the  first  to  fourth  annual  reports 
of  Texas  Geological  Survey,  especially  under  county  descriptions. 

Utah 

The  writer  has  not  seen  any  published  information  of  value  regard- 
ing the  clay  resources  of  this  State.  Common  brick-clays  are  to  be  found 
at  many  points,  and  at  the  St.  Louis  Exposition  there  were  exhibited 
samples  of  fire-bricks  and  crucibles  made  by  the  Utah  Fire-clay  Com- 
pany of  Salt  Lake  City,  while  kaolin  samples  were  shown  from  Millard 
County  and  Lehi. 

Virginia 
Residual  Clays 

The  crystalline  rocks,  consisting  of  granite,  gneisses,  and  schists  with 
some  intrusives  extend  across  ths  State  from  north  to  south  in  a  belt  of 
increasing  width,  whose  western  boundary  follows  approximately  a  line 
running  from  Harper's  Ferry  southwestward,  passing  a  few  miles  east 
of  Front  Royal.  The  eastern  edge  coincides  approximately  with  the 
"Fall-line."  Residual  clays  are  not  uncommon  throughout  this  area, 
but  they  are  usually  impure;  and  adapted  to  little  else  but  common 
brick. 

Kaolin  is  found  in  Henry  and  Patrick  counties  and  some  promising 
deposits  have  been  developed  in  the  former  (PL  XXXIX,  Figs.  1  and  2). 

The  Cambro-Silurian  shales  and  limestones  yield  an  abundance  of 
impure  residual  clay,  which  is  well  adapted  to  brick  manufacture.  These 
clays,  which  are  likely  to  be  used  throughout  the  Great  Valley  region, 
are  all  red-burning  so  far  as  known. 


PLATE  XXXIX 


FIG.  1. — View  of  kaolin-pit  near  Oak  Level,  Va. 
clearly  contrasted  to  the  white  kaolin. 


The  ferruginous  clay  walls  are 
(Photo  by  H.  Ries.) 


FIG.  2. — General  view  of  kaolin  washing  plant  near  Oak  Level,  Va.     The  crude  clay 
is  washed  down  the  trough  from  the  mine.     (Photo  by  H.  Ries.) 

435 


NORTH  DAKOTA  TO  WYOMING  437 

Carboniferous 

Though  containing  important  beds  of  coal,  the  clayey  members  of 
this  formation  in  southwestern  Virginia  have  received  but  little  notice, 
but  it  seems  highly  probable  that  they  contain  shale-deposits  of  sufficient 
value  for  making  vitrified  wares,  and  even  now  they  are  successfully 
worked  at  one  locality,  namely,  Millhall. 

Triassic 

The  Triassic  shales  associated  with  the  coals  of  the  Richmond  basin 
have  not  proven  of  any  value  for  the  manufacture  of  clay-products. 

Tertiary 

The  Tertiary  and  Pleistocene  formations  of  the  coastal-plain  area 
have  received  the  most  attention  by  clay-workers  in  the  State. 

The  Tertiary  beds  consist  of  a  series  of  clays,  sands,  marls,  sand- 
stones, and  greensands,  which  dip  gently  to  the  southeast,  and  are  over- 
lain by  later  formations. 

The  clay-deposits,  which  are  of  Miocene  age  and  usually  of  lenticular 
character,  are  most  abundant  towards  the  northwestern  border  of  the 
coastal  plain,  and  have  been  noted  near  Richmond,  Bermuda  Hundred, 
Curie's  Neck,  etc.  They  are  red-burning  and  often  yield  a  vitrified 
body,  but,  although  to  be  ranked  as  among  the  best  clays  in  the  State, 
they  are  little  used. 

Some  promising  Eocene  clays  are  known  between  Fredericksburg 
and  Stafford  Court  House. 

The  diatomaceous  earths  form  an  extended  series  of  deposits  along 
the  Rappahannock  River  and  around  Richmond,  but  they  are  worked 
at  but  one  locality,  namely,  Wilmont  (PL  XL,  Fig.  1),  to  make  boiler- 
setting  brick  and  fireproofing. 

Pleistocene 

Pleistocene  clays  occur  at  a  number  of  points,  but  the  deposits  are,  with 
few  exceptions,  of  shallow  character  and  the  material  red-burning.  The 
clays  are  extensively  dug  around  Richmond  for  common-brick  manu- 
facture, as  well  as  at  Norfolk,  Suffolk,  Petersburg,  and  several  points 
along  the  James  River  (PL  XL,  Fig.  2).  A  semi-refractory  Pleistocene 
clay  is  found  near  Wilmont  on  the  Rappahannock. 

Around  Alexandria  the  Columbian  loams  are  worked  on  a  large  scale 
for  the  manufacture  of  common  and  pressed  brick,  which  supply  the 
Washington  market. 

The  following  table  contains  the  analyses  and  physical  tests  of  some 
of  the  coastal-plain  clays : 


438 


CLAYS 


OcO^iOcOt^-OS 
00  t>-  ro  co  O  O  OS 

frj 

oo 


c^^ooupoci^r^co 
3 


rH  COO  OO  TH  O  OOO 
(N  rH 


OS  OS  Ot^  rH  rH  ^  X 


OS  ?C  t^  rH  rH 


Tf  00  OS  <N  <N  t^  rH  CM  rH 

90OCQCDi-4f-lt»C100 

ro  »o  co  o  o  c<i  o  -—  i  <N 


CO  CO  "5  X  X  Tf  rH  00  C 
oo^-loOrot^TtioOc 


M    O   rH   rH   M    O  O  "* 


OS  iMJSrOTFrHOrHOO-^rHlOOCr; 

os      co          co      »o      rf      Tf      co 


".••3 

os      co<So5ioooc<Mcoi 


"3  _,  ^  ~     r- 

o.        os  -gjCO  OCCOOS        X        ^*  §  ^  "Q 

§     ^^^^^2^°°^^  ®  >  ^ 


OS  OS^T^OC  I^t-rHCOiC 


.        ^o§. 

<3^          rvj    feC         rH  r_i'~'r4"  ^ 


os 

<M 


,00  OQ  o  o  »o  c<  o  o  •<** 


o  »o  c< 

(N  rH 


00  t^  iO  i—i  c^J  00  ^t1  :O 


6    6       3 


•i  I 

58   §^ 

.«     la 


-,  J ! 

5   II  1 


s     g^ 


am 


PLATE  XL 


FIG.   1. — Section  showing  diatomaceous  earth   (Miocene)  overlain  by  Pleistocene 
clay,  Wilmont,  Va.     (After  H.  Ries,  Va.  Geol.  Surv.,  Bill.  II,  p.  175,  1606.) 


FIG.   2. — Pleistocene   brick  and   tile-clay   underlying  terrace,   Oldfield    on    James 
River,  Va.     (After  H.  Ries,  Va.  Geol.  Surv.,  Bull.  II,  p.  166,  1906.) 

439 


NORTH  DAKOTA  TO  WYOMING  441 

References  on  Virginia  Clays 

1.  Fontaine,  W.  M.,  The  Potomac  Formation  in  Virginia,  U.  S.  Geol. 
Surv.,  Bull.  145,  1896. 

2.  Ries,  H.,  A  Preliminary  Report  on  a  Part  of  the  Clays  of  Virginia. 
Va.  Geol.  Surv.,  Bull.  II,  1906. 

3.  Ries,  H.,  The  Clays  of  the  United  States,  East  of  the  Mississippi 
River,  U.  S.  Geol.  Surv.,  Prof.  Pap.  11. 

Washington 

No  systematic  account  of  the  Washington  clays  has  been  printed, 
and  the  few  published  references  are  scant  and  unsatisfactory. 

The  deposits  are  divisible  into  (1)  Clay-shales,  (2)  Residual  clays, 
and  (3)  Glacial  clays. 

Clay-shales. — These  appear  to  be  chiefly  of  Tertiary  age.  Flint-clay 
and  sewer-pipe  clay,  interbedded  with  sandstone  and  coal,  occur  at 
Kummer  and  Taylor  on  the  Columbia  and  Puget  Sound  Railroad,  and 
are  mined  for  making  fire-brick,  sewer-pipe,  etc.  Tertiary  fire-clays  are 
also  found  two  miles  east  of  Little  Falls  station,  while  clays  suitable 
for  brick,  terra-cotta,  and  stoneware  are  dug  at  Clayton,  30  miles  north 
of  Spokane.  Others  are  known  at  Sopenah  and  stoneware-clays  are 
obtained  near  the  town  of  Palouse. 

Residual  clays. — Deposits  of  this  type  occur  only  in  the  non-glaciated 
part  of  the  State.  In  western  Washington,  between  Puget  Sound  and 
the  Columbia  River,  these  clays  are  very  thick  in  places,  and  derived 
from  the  weathering  of  shale.  A  residual  basalt  clay  is  used  for  red 
brick  in  eastern  Washington. 

Glacial  clays. — The  glacial  clays  are  widely  distributed  over  the  glaci- 
ated area  of  Washington.  Brick  plants  are  located  close  to  the  larger 
centers  of  population  and  on  the  shores  of  the  Sound.  The  clays  are 
mostly  red-burning. 

References  on  Washington  Clays 

1.  Landes,  H.,  Clay-deposits  of  Washington,  U.  S.  Geol.  Surv.,  Bull. 
260,  p.  550,  1905. 

2.  Landes,  H.,  Wash.  Geol.  Surv.,  Ann.  Rept.,  Vol.  I,  p.  172,  1902. 


442  CLAYS 

West  Virginia l 

With  the  exception  of  a  few  Pleistocene  deposits,  the  clay-bearing 
formations  of  West  Virginia  are  all  of  Palaeozoic  age. 

Silurian 

The  residual  clays  derived  from  the  Shenandoah  limestone  are 
found  over  large  areas  in  Berkeley,  Jefferson,  and  parts  of  Hardy,  Hamp- 
shire, and  Pendleton  counties;  they  have  been  worked  at  Charlestown 
and  Shepherdstown  for  red  brick. 

The  shales  of  this  age,  known  as  the  Martinsburg  shale  from  their 
type  occurrence  at  the  town  of  that  name,  are  hard  and  slaty  when 
fresh,  but  weather  down  to  a  clayey  mass  which  can  be  used  for  red-brick 
manufacture. 

Red  shales  of  Medina  age  and  brown  and  gray  Clinton  shales  outcrop 
in  belts  along  the  mountain-slopes  of  Mineral,  Grant,  Hardy,  and  Pendle- 
ton counties,  but  are  not  favorably  located  for  working . 

Devonian 

The  Devonian  formations,  according  to  Grimsley,  consist  of  sand- 
stones and  shales,  being  found  in  Mineral,  Grant,  Hardy,  Pendleton, 
Preston,  Tucker,  Randolph,  Pocahontas,  Greenbrier,  and  Monroe  coun- 
ties. They  are  grouped  under  the  Hamilton,  Chemung,  and  Catskill 
formations.  Many  of  them  are  adapted  to  brick  manufacture,  but  they 
are  worked  only  at  Elkins,  Randolph  County. 

Lower  Carboniferous 

The  Mauch  Chunk  shales,  consisting  of  red  and  grayish-blue  shales, 
green  sandstones,  and  a  few  thin  limestones,  form  a  belt  extending 
across  the  State  from  Preston  County,  through  Tucker,  Randolph, 
Pocahontas,  Greenbrier,  Monroe,  and  Summers  counties. 

The  red  shales  and  their  residual  clays  form  an  excellent  material 
for  making  red-pressed  brick,  the  deposits  moreover  being  well  located, 
but  up  to  the  present  time  they  have  not  been  utilized. 

Carboniferous 

Pottsville  series. — This  contains  clays,  shales,  sandstones,  conglomer- 
ates, and  coal-beds,  but  the  only  clay  thus  far  worked  is  that  occurring 
beneath  the  Homewood  sandstone  and  known  as  the  Mount  Savage 

1  Grimsley,  G.  P.,  W.  Va.  Geol.  Surv.,  Ill,  1906. 


PLATE  XLI 


FIG.    1. — Red-burning   brick-clay   bank   at    Freeman,   Wash.      (Photo    loaned   by 
Washington  Brick,  Lime,  and  M'f'g  Co.) 


FIG.  2. — Shale-bed  of  Mahoning  horizon,  Charleston,  W.  Va.     The  shale  is  blue 
and  red  with  some  fire-clay  mixed  through  it.     (After  Grimsley,  W.  Va.  Geol. 

Surv.,  Ill,  1906.) 

443 


NORTH  DAKOTA  TO  WYOMING  445 

fire-clay.  This  is  mined  at  Piedmont  for  fire-brick  manufacture,  and 
consists  of  both  plastic  and  flint  fire-clay,  the  two  forming  a  bed  about 
15  feet  thick. 

Allegheny  series. — In  this  series  there  are  found  a  number  of  im- 
portant coal-seams  with  their  underlying  fire-clays,  the  two  important 
groups  being  the  Kittanning  coals  and  clays,  and  the  Freeport  group 
of  coals  and  clays. 

The  two  most  valuable  beds  of  fire-clay  are  the  Lower  Kittanning 
and  the  Bolivar. 

The  shales  in  the  series  have  also  been  successfully  used  for  building- 
brick. 

Clarion  clay. — The  Clarion  coal  at  the  base  of  the  Allegheny  series 
is  often  underlain  by  a  thick  bed  of  fire-clay,  but  it  is  not  worked  in  West 
Virginia. 

Kittanning  clays. — The  Lower  Kittanning  coal  is  very  persistent 
through  Ohio  and  Pennsylvania,  but  in  West  Virginia  it  is  absent  en- 
tirely as  a  workable  bed  in  many  regions  of  the  State,  and  its  place  taken 
by  the  fire-clay. 

The  Lower  Kittanning  clay  under  the  coal  of  that  name  is  5  to 
15  feet  at  Hammond  where  it  is  worked. 

Between  the  Upper  and  Lower  Kittanning  coals  is  an  interval  of 
sandstone,  which  at  New  Cumberland  and  Hammond  carries  the  Middle 
Kittanning  coal  and  its  underlying  fire-clay. 

At  New  Cumberland,  which  is  the  largest  brick-manufacturing  center 
in  the  State,  the  Lower  and  Middle  Kittanning  clays  are  employed  for 
the  manufacture  of  building-brick  and  paving-blocks,  and  the  Lower 
Kittanning  clays  for  sewer-pipe.  The  shales  between  these  two  were 
formerly  burned  into  common  brick. 

The  following  section  at  the  Globe  Works,  given  by  Grimsley,  is 
stated  by  him  to  be  fairly  typical  of  this  region: 

Feet.  Inches. 

Sandstone 40 

Coal 2  6 

Flint-clay 6 

Gray  shale-clay 4 

Blue  shale-clay 12 

Sandstone  floor 4 

Fine  laminated  shales 40 

Coal  (Lower  Kittanning) 3 

Clay  (Lower  Kittanning) 10 

The  bottom  clay  is  used  for  sewer-pipe,  while  the  flint-clay  and  blue 
and  gray  shales  are  mixed  together  for  brick  and  paving-blocks. 


446  CLAYS 

Upper  Freeport  clay. — There  are  some  good  outcrops  of  this  clay 
on  Decker's  Creek  above  Morgan  town  near  Dellslow,  with  good  rail- 
road connection,  and  could  be  easily  developed. 

Conemaugh  series. — This  series  consists  chiefly  of  sandstones  and 
limestones,  but  contains  scattered  shale-deposits  and  some  fire-clay. 
Overlying  the  Upper  Freeport  coal,  or  at  times  separated  from  it  by  the 
dark  fossiliferous  Uffington  shales,  are  the  Lower  and  Upper  Mahoning 
sandstones.  They  are  seen  from  Upshur  southwest  into  Mingo,  western 
Wyoming,  and  Raleigh  counties.  Between  the  two  there  is  of  ten  found 
the  Mahoning  coal,  which  is  worked  near  New  Cumberland,  while  under 
the  coal,  and  sometimes  replacing  it,  there  is  a  good  bed  of  fire-clay 
found  in  a  few  regions  and  mined  at  Thornton,  where  it  shows  18  feet 
of  flint  and  soft  clay.  Near  Ceredo,  Wayne  County,  the  clay  is  present 
without  the  coal. 

At  many  points  a  shale-bed  occurs  between  the  two  sandstones, 
Those  worked  around  Charlestown  may  belong  in  part  to  this  horizon, 
although  some  of  the  beds  have  been  doubtfully  referred  to  the  Kanawha 
series  of  Virginia. 

Overlying  the  Mahoning  sandstone  is  the  Cambridge  limestone 
followed  by  the  Ames  limestone,  and  between  these  two  is  a  mass  of 
Pittsburg  red  shales,  30  to  100  feet  thick,  which  extend  from  the  Penn- 
sylvania line  southward  to  the  Big  Sandy  River.  These  shales,  which 
will  undoubtedly  prove  of  economic  value,  are  as  yet  used  only  at  Kunt- 
ington  for  roofing-tile  manufacture.  They  also  occur  at  Barlow,  Charles- 
town,  etc. 

In  Preston  County  near  Reedsville,  Masontown,  and  Kingwood,  as 
well  as  near  Collier  and  Wellsburg  in  Brooke  County,  the  shales  are 
partly  replaced  by  the  Saltzburg  sandstone.  Overlying  the  Ames  lime- 
stone is  the  Birmingham  shale. 

A  very  complete  section  of  the  Conemaugh  series  is  exposed  at 
Morgan  town,  Monongalia  County,  but  the  only  shales  worked  are  the 
Pittsburg  ones.  They  make  a  building-  and  paving-brick. 

Monongahela  series. — A  series  of  coals,  limestones,  sandstones,  and 
shales  are  included  in  this  group,  the  general  section  being  well  exposed 
in  Pinnickinnick  Hill  at  Clarksburg.  The  Pittsburg  coal  at  the  base 
of  the  Monongahela  is  an  important  and  well-recognized  horizon.  At 
Clarksburg  the  shales  underlying  and  overlying  this  coal-seam  are 
worked  for  building-  and  paving-brick. 

The  shales  worked  near  Spilman  for  paving-blocks  and  building- 
brick  lie  near  the  top  of  the  Monongahela  series,  and  those  at  Mounds- 
ville  are  also  near  this  horizon. 


1 


6    e8 


o 


1 

6D 
.f 


NORTH  DAKOTA  TO  WYOMING 


449 


Dunkard  or  Permo-carboniferous. — The  rocks  of  this  age  cover  a  belt 
40  to  60  miles  wide,  bordering  the  Ohio  River.  They  include  a  number 
of  utilizable  shales,  but  at  present  they  are  being  worked  only  at  Parkers- 
burg,  Wood  County,  for  making  roofing-tile. 

Pleistocene 

A  number  of  brick  plants  in  the  State  obtain  their  raw  material 
from  deposits  near  creeks  or  rivers.  These  clays  underlie  terraces 
and  occur  either  near  the  present  river-level  or  a  number  of  feet  above 
it.  The  former  are  flood-plain  deposits  built  up  by  the  rivers  in  recent 
times,  while  the  latter  represent  the  remnants  of  lake-beds  formed  when 
the  valleys  were  dammed  by  ice,  thus  giving  rise  to  the  formation  of 
temporary  lakes.  The  clays  of  the  Monongahela,  Teays,  and  adjacent 
valleys  are  of  the  second  type. 

ANALYSES  OF  WEST  VIRGINIA  CLAYS 


L* 

II. 

III. 

IV. 

V. 

VI. 

Silica  (SiO2)     

54.35 

57.75 

58.78 

56.3 

61.44 

52.24 

Alumina,  (A^Os)                   . 

21  49 

20.17 

22.57 

19  07 

26  18 

29  28 

Kerric  oxide  (FeoOa) 

8 

7.00 

4.13 

9  58 

0  30 

2  73 

Ferrous  oxid.6  (FeO)            .... 

0.33 

1.40 

0.36 

0  51 

Lime  (CaO)                       

0.30 

0.22 

0.18 

0  69 

0  12 

0  68 

Magnesia  (MgO)           

0.79 

1.22 

1.00 

2.01 

0  2 

Soda  (Na2O)                  

trace 

0.62 

0.54 

6.02 

0  37 

Potash  (KoO)                    

6.35 

2.59 

3.15 

2.11 

Titanic  oxide  (TiOo)  

0.86 

0.87 

1.03 

0.71 

1.39 

1.2 

Moisture                            

1.62 

2.75 

1.05 

0.77 

1.28 

Phosphoric  acid  (PoOr) 

0  09 

0  09 

0  35 

0  01 

0  07 

Sulphur  trioxide  (SOa)  

trace 

Ignition          

5.70 

5.94 

5.43 

8.01 

9.07 

10.12 

Total  

99.55 

99.55 

99.61 

96.37 

99.66 

100.79 

VII. 

VIII. 

IX. 

X. 

XI. 

XII. 

Silica  (SiO2) 

57.58 

59.76 

57.52 

57.89 

66  69 

56  19 

Alumina  (A^Os)                   

21.41 

22.79 

21.76 

21.59 

21  83 

26  31 

Ferric  oxide  (Fe->Os)         

3.75 

0.60 

3.41 

5.62 

0  37 

2  82 

Ferrous  oxide  (FeO)  

3.45 

3.53 

3.7 

1.26 

1.00 

0  96 

Lime  (CaO)   .            

0.46 

0.59 

0.60 

0.61 

0.33 

0  39 

Magnesia  (MgO)  

1.44 

1.23 

0.88 

1.55 

0.10 

1  44 

Soda  (Na.,O) 

0  1 

0.42 

0.03 

0  29 

0  08 

0  50 

Potash  (K2O)                        

3.14 

3.79 

3.57 

3.28 

0  48 

3  90 

Titanic  oxide  (TiO->)   

0.84 

0.82 

0.83 

0.72 

1  11 

0  63 

Moisture        .                   

0.38 

0.54 

0.86 

1.27 

0  99 

1  39 

Phosphoric  acid  (PoOr) 

0  11 

0  46 

0  14 

0  21 

trace 

trace 

Sulphur  trioxide  (SOs)  

Ignition        

7.25 

5.26 

7.27 

6.18 

7.13 

5  48 

Total                    

99.91 

99.79 

100  .  57 

100  47 

100  11 

100  01 

*  For  references  see  foot  of  table,  p.  450. 


450 


CLAYS 


AXALYSES  OF  WEST  VIRGINIA  CLAYS — Continued 


XIII. 

XIV. 

XV. 

XVI. 

XVII. 

Silica  (SiO->)                          

55.63 

58.28 

50.80 

68.42 

63.88 

Alumina  (Al-iOs)   

20.76 

21.26 

19.47 

16.38 

17.18 

Ferric  oxide  (Fe-)Oa)  

3.94 

1.87 

8.83 

3.05 

5.72 

Ferrous  oxide  (FeO) 

4  17 

3.37 

1.9 

1.89 

0  50 

Lime  (CaO)                                       .    . 

0.86 

0.78 

1.51 

0.94 

"  0  16 

Magnesia  (MgO)                 

1.70 

1.35 

1.74 

1.8 

1  3 

Soda  (NaoO)                 

0.34 

0.39 

0.89 

0.63 

0.6 

Potash  (KoO)             

2.97 

2.87 

2.24 

0.93 

2.29 

Titanic  oxide  (TiOo) 

0  98 

0  86 

0  68 

0  88 

0  87 

1.03 

1.30 

0.6 

1.76 

Phosphoric  acid  (P'-Ot)           

0.23 

0.39 

0.2 

0  08 

0  36 

Sulphur  trioxide  (SOs)  

trace 

6.98 

6.84 

11.37 

4  58 

5  60 

Total  

99.59 

99.56 

100  .  23 

99.58 

100  22 

PHYSICAL  TESTS  OF  WEST  VIRGINIA  CLAYS 


I. 

II. 

III. 

V. 

VI. 

VII. 

VIII. 

Water  required   per  cent.  .  . 

28 

25 

2  1 

28 

24 

°6 

Tensile  strength,  Ibs.  per  sq.  in.  . 
Air-shrinkage,  per  cent.  .  
Cone  of  incipient  vitrification  .  .  . 

122 
4 
1 

34 
3.5 

32 
3 

58 
4 

40 
4 
1 

46 

4 
1 

Cone  of  vitrification  

5 

5 

1 

26 

5 

,5 

Cone  of  viscosity 

5  + 

30  + 

28 

Fire-shrinkage  per  cent. 

11 

10 

2 

6 

6 

Color  when  burned 

red 

red 

buff 

buff 

brown 

brown 

IX. 

X. 

XI. 

XII. 

XIII. 

XIV. 

XVII. 

Water  required,  per  cent  
Tensile  strength,  Ibs.  per  sq.  in.  . 
Air-shrinkage,  per  cent  

26 
40 

3  5 

27 
36  I 
4 

20 
75  to 
90 
4 

24 
89  to 
100 
4 

22 
|  109 
4  5 

25 

78 
4  5 

32 
140 

Q 

Cone  of  incipient  vitrification  .  .  . 

1 

1 

1 

1 

1 

Cone  of  vitrification. 

5 

5 

30 

K. 

1 

K 

K 

Cone  of  viscosity  

5 

Fire-shrinkage,  per  cent  
Color  when  burned  

10 

red 

8 
red 

0 
buff 

6 
red 

2 

red 

red 

12 
red 

II. 
III. 

IV. 

V. 

VI. 

VII. 

VIII. 

IX. 


xx!l: 

XIV. 

XV. 

XVI. 

XVII. 

Nos 
Surv. 


Residual  limestone  clay,  Charlestown,  Silurian. 

Residual  shale-clay,  Martinsburg,  Silurian. 

Shale,  Elkins,  Randolph  County,  Hamilton. 

Shale,  Decker's  Creek  near  Morgantown,  Mauch  Chunk. 

Fire-clay,    Piedmont,  Mount  Savage  clay. 

Flint-clay    "* 

Gray  shale 

Blue  shale 


Shale 


Clifton  Mine,  New  Cumberland,  Middle  Kittanning. 
mine,  New  Cumberland,  Lower  Kittanning.   % 


ay   f  Thornt°".  in  Conemaugh  series,  Mahoning  coal  horizon. 
Shale,  Morgantown,  Pittsburg  red  shale. 
Blue  shale,  Huntington,  Conemaugh  series. 
Mixture  of  Spilman  shales,  Spilman,  Conemaugh  series. 
Parkersburg,  Dunkard  shale. 
River-clay,  Parkersburg,  Pleistocene. 
I-XVII   selected  by  Dr.  Grimsley  as  representative  ones,  from  Vol.  Ill,  W.  Va.  Geol. 


NORTH  DAKOTA  TO  WYOMING 


451 


References  on  West  Virginia  Clays 

1.  Grimsley,  G.  P.,  The  Clays  of  West  Virginia,  W.  Va.  Geol.  Surv., 
Ill,  1906. 

2.  White,   I.    C.,    Correlation    Papers,    Carboniferous,    U.   S.   Geol. 
Surv.,  Bull.  65. 


LEGEND 

K\\\\]  Lacustrine  and  glacial  clays. 
|  |  Estuarin*  and  glacial  cloys. 

II  I  I  I  |  MI  Loess  Residutfl  and  .stream  clays 
irTtlTTTI  mostly  red  burning. 

II  HI  |  I  ||  Glacial  and  stream  clays 
II  III  I  I  II       mostly  red  burning. 

1  Residual  clays  red  burning. 

HH  Cincinnati  Shales  mostly  cream  burning. 


FIG.    64. — Map    of   Wisconsin,   showing  distribution    of    clay-bearing  formations. 
(Adapted  from  Buckley,  Wis.  Geol.  and  Nat.  Hist.  Surv.,  Bull.  VII,  1901.) 

Wisconsin 

In  this  State  the  clay-deposits  belong  to  formations  representing 
somewhat  the  two  extremes  of  the  geological  column.    Those  belonging 


452  CLAYS 

to  the  older  formations  are  nearly  all  of  residual  character,  while  those 
belonging  to  the  sedimentary  deposits  are  of  very  recent  geologic  age. 
It  seems  best,  therefore,  to  divide  them  into  two  groups,  namely,  the 
residual  clays  and  the  sedimentary  clays. 

Residual  Clays 

These  have  been  derived  from  a  variety  of  rocks,  including  granites 
and  gneisses,  greenstones  and  allied  volcanic  rocks,  limestone  and 
dolomite,  sandstone  and  shale. 

Pre-Cambrian  residuals.— These  occur  at  a  number  of  points  in 
the  central  part  of  the  State,  in  Eau  Claire,  Jackson,  Wood,  Portage, 
Marathon,  and  Clark  counties.  They  are  usually  gritty  clays  which 
have  been  formed  by  the  decomposition  of  schists  or  gneisses,  and  vary 
in  depth  from  perhaps  2  or  3  feet  to  as  much  as  40.  Although  some- 
times reaching  nearly  to  the  surface,  they  are  at  other  times  covered 
by  a  bed  of  Potsdam  sandstone  which  has  apparently  protected  them 
from  erosion.  Deposits  of  this  occur  in  the  vicinity  of  Grand  Rapids, 
Eau  Claire,  Black  River  Falls,  Stevens  Point,  Abbotsford,  etc.  They 
are  nearly  all  red-burning,  and  while  refractory  ones  low  in  iron  are 
known  to  occur,  the  deposits  of  them  so  far  as  found  are  rather  small. 
Their  main  use  is  for  the  manufacture  of  common  brick,  but  at  Halcyon 
near  Black  River  Falls  the  material  has  been  found  adapted  to  the 
manufacture  of  dry-press  brick  and  even  paving-brick. 

Potsdam  shales. — In  a  few  localities  there  occurs  at  the  base  of  the 
Potsdam  a  tough  plastic  clay  which  has  been  derived  by  the  weathering 
of  a  siliceous  shale.  This  material  has  been  exposed  near  Merrillan, 
Durand,  and  other  points,  but  has  not  been  utilized  to  any  extent  for 
the  manufacture  of  clay-products. 

Ordovician  limestone  residuals. — Within  the  driftless  area  of  Wis- 
consin the  cherty  galena  limestone  is  found  weathered  in  its  upper 
portion  to  sandy  residual  clay  containing  many  flint  fragments  scattered 
through  it.  Up  to  the  present  time  it  has  not  been  used  for  the  manu- 
facture of  common  brick  to  which  it  is  chiefly  adapted,  nor  is  there 
any  likelihood  of  its  ever  becoming  of  any  importance. 

Sedimentary  Clays 

Hudson  River  shale. — This  shale  forms  a  narrow  belt  in  the  eastern 
part  of  Wisconsin  which  extends  from  the  southern  boundary  of  the 
State  up  to  Green  Bay.  In  this  State  it  is  not  very  well  adapted  to  the 
manufacture  of  brick,  but  on  weathering  breaks  down  rather  easily  to  a 
yellow  clay  which  has  very  fair  plasticity  and  is  usually  red-burning. 


PLATE  XLIII 


FIG.  1.— Pit  of  estuarine  clay,  Fort  Atkinson,  Wis.     The  flat  area  is  underlain 
by  clay,  while  the  surrounding  low  hills  are  of  sand.     (Photo  by  H.  Ries.) 


FIG.  2. — Pleistocene  brick-clay,  Milwaukee,  Wis.     The  mound  in  middle  of  pit  is 
sand  and  is  left  standing.     (Photo  by  H.  Ries.) 

453 


NORTH  DAKOTA  TO  WYOMING  455 

The  material  has  been  worked  at  Stockbridge,  Calumet  County,  and  at 
Oakfield,  Fond  du  Lac  County,  for  the  manufacture  of  brick.  At  the 
former  locality  a  mixture  of  the  weathered  shale  and  the  partly  weathered 
material  is  used  with  excellent  results.  A  second  area  of  these  shales  is 
known  to  occur  in  Lafayette  County,  to  the  east  and  southeast  of  Platt- 
ville,  where  the  material  is  to  be  found  around  the  base  of  the  Mound 
Hills  so  prominent  in  that  region.  It  weathers  to  a  yellow  clay  of  high 
plasticity  and  one  which  burns  to  a  very  hard  body  of  excellent  red  color. 

Pleistocene  Clays 

The  Pleistocene  clays  of  Wisconsin  have  been  grouped  by  Buckley 
(Ref.  1)  as  follows:  1.  Lacustrine  deposits;  2.  Stream  deposits;  3. 
Estuarine  deposits,  and  4.  Glacial  clays. 

Lacustrine  deposits. — These  respresent  a  very  extensive  type,  and 
were  laid  down  during  the  former  inland  extension  of  the  Great  Lakes, 
so  that  they  are  now  often  found  some  distance  from  the  present  lake 
shore.  Thus,  around  Racine,  they  occur  18  miles  inland.  They  are 
also  found  at  Sheboygan,  over  parts  of  Door  County,  and  in  parts  of 
Manitowoc,  Calumet,  and  Fond  du  Lac  counties;  much  of  Green  Lake, 
Waushara,  and  Waupaca  counties  too  are  underlain  by  them,  while  to 
the  north  they  are  found  as  far  as  Shawano.  These  lacustrine  deposits, 
adjoining  Lake  Michigan  on  the  east  and  Lake  Superior  on  the  north,  are 
an  important  source  of  cream-burning  brick-clays,  and  the  beds  often 
exceed  100  feet  in  thickness.  Sometimes  the  upper  few  feet  burn  red, 
owing  to  the  fact  that  the  carbonate  of  lime  has  been  leached  out  of 
them.  Around  Green  Bay,  Manitowoc,  and  Racine  these  clays  are  much 
used  for  the  manufacture  of  common,  pressed  brick  and  drain-tile,  but 
they  are  of  little  value  for  anything  else. 

Estuarine  clays. — These  include  all  the  clays  of  eastern  Wisconsin 
which  are  underlain  by  limestone  and  have  been  modified  by  glacial  action. 
They  were  formed  at  the  same  time  and  in  association  with  the  lake- 
deposits,  but  differ  from  them  usually  in  showing  a  more  variable  lime- 
content  and  burn  hard  and  dense  at  a  lower  temperature.  Thus,  for 
example,  the  lake-clays  apparently  have  to  be  burned  up  to  cone  3,  while 
the  estuarine  clays  can  be  burned  at  cone  05  to  1.  These  estuarine 
deposits  are  found  along  the  Fox,  Wolf,  Rock,  Wisconsin,  Eau  Claire, 
Chippewa,  Black,  Red,  Cedar,  and  many  other  rivers  in  the  eastern,  north- 
eastern, and  southern  parts  of  the  State. 

Glacial  clays. — These  have  been  deposited  over  a  large  part  of  the 
northern  half  of  the  State  and  include  a  series  of  deposits  of  uncertain 
extent  and  variable  character  and  thickness.  In  some  places  they 


456 


CLAYS 


consist  of  bowlder-clay  and  are  therefore  of  a  very  stony  character,  while 
at  others  they  may  represent  deposits  that  have  been  formed  in  temporary 
lakes  during  the  last  glacial  epoch.  Those  worked  at  Athens  belong  to 
the  former  type,  and  those  worked  at  Menomonie  and  forming  the  basis 
of  an  extensive  local  industry  belong  to  the  latter  type.  Under  this 
heading  we  should  perhaps  also  include  the  silty  loess-clays  which  cover 
a  large  area  in  the  western  part  of  the  State  and  are  worked  at  Platteville, 
Menomonie,  La  Crosse,  and  other  places.  They  represent  a  good  char- 
acter of  clay,  which  in  many  instances  is  used  only  for  common  brick, 
but  is  also  adapted  to  the  manufacture  of  dry-press  brick. 
ANALYSES  OF  WISCONSIN  CLAYS 


I. 

II. 

III. 

IV. 

V. 

Silica  (SiO2)  

64.50 

62.59 

35.93 

48.39 

44.18 

Alumina  (Al2Oa)  

26.20 

17.42 

11.75 

12.50 

10.83 

Ferric  oxide  (Fe2Os)  

0.07 

5.88 

4.08 

5.40 

3.30 

Lime  (CaO) 

none 

12  43 

10  88 

14  05 

Magnesia  (MgO).  . 

1.24 

9  92 

4  82 

5  91 

Potash  (K2O)            .      . 

0.31 

8.08 

2  46 

3  90 

3   10 

Soda  (Na2O)             

0.52 

1.24 

0  68 

0  70 

Loss  on  ignition       

8.90 

4.15 

22.06 

13.02 

17  34 

Titanic  acid  (TiO2)  

0.30 

0  30 

0.43 

0  30 

Manganese  oxide  (MnO).  .  .  . 

SO3  trace 

0.10 

trace 

VI. 

VII. 

VIII. 

IX. 

X. 

Silica  (SiO2)  .  .  . 

40  17 

31  90 

71  77 

65  44 

69  86 

Alumina  (Al2Os).  .  . 

9  14 

8  74 

13  74 

13  51 

13  55 

Ferric  oxide  (FezOs).   .  .  . 

3  00 

3  00 

3  60 

5.40 

5.46 

Lime  (CaO)  
Magnesia  (MgO)  

14.49 

8  34 

17.06 
10.63 

1.23 
1  17 

2.95 
2.20 

0.71 
1.43 

Potash  (K2O) 

3  06 

2  20 

2  30 

3  44 

2  36 

Soda  (Na2O) 

0  34 

0  82 

1  20 

1  54 

1  78 

Loss  on  ignition 

21  37 

25  19 

5  00 

4  69 

4  40 

Titanic  acid  (TiO2)  
Manganese  oxide  (MnO).  .  .  . 

0.35 
0.09 

0.25 
0.19 

0.45 
trace 

0.60 
trace 

0.77 
trace 

LOCALITIES  OF  THE  ABOVE 


No. 

Locality. 

Geological  Age. 

Uses. 

I. 

Hersey.  . 

Residual 

Not  worked 

II. 

Merrillan  

Potsdam  

i  (          (i 

III. 

Oakfield  

Hudson  

Common  brick 

IV. 

Green  Bay.  . 

Pleistocene 

Br  ck 

V. 

(  i        (i 

n 

VI. 

Milwaukee  

(i 

i 

VII. 

Watertown  

1  1 

i 

VIII. 

Chippewa  Falls  

Glacial 

i 

IX. 

Menomonie  

1  1 

Pressed  brick 

X. 

Whittlesey  

e  i 

Brick 

Nos.  I-X  from  Wis.  Geol.  and  Nat.  Hist.  Surv.,  Bull.  7,  1901. 


NORTH  DAKOTA  TO  WYOMING'  457 

References  on  Wisconsin  Clays 

1.  Buckley,  E.  R.,  The  Clays  and  Clay  Industries  of  Wisconsin,  Wis. 
Geol.  and  Nat.  Hist.  Surv.,  Bull.  7,  Pt.  I,  1901. 

2.  Chamberlain,  T.  C.,  Geol.  of  Wis.,  I,  p.  669. 

3.  Irving,  R.  D.,  On  the  Kaolins  of  Wisconsin,  Wis.  Acad.  Arts  and 
Letters,  Trans.,  1876. 

4.  Irving,  R.  D.,  Geol.  Wis.,  II,  p.  630. 

5.  Irving,  R.  D.,  Mineral  Resources  of  Wisconsin,  Amer.  Inst.  Min. 
Eng.,  Trans.,  VIII,  p.  478. 

6.  Ries,  H.,  Clays  of  Wisconsin,  Mining  World,  Mar.  25,  1905.     See 
also  forthcoming  bulletin,  Wis.  Geol.  and  Nat.  Hist.  Surv. 

7.  Sweet,  E.  T.,  Milwaukee  Clay,  Amer.  Jour.  Sci.,  iii,  XXIV,  p.  154. 

Wyoming 

Little  is  known  regarding  Wyoming  clays,  owing  largely  to  their  lack 
of  development.  W.  C.  Knight  says:1  "  So  far  as  is  known,  the  clays 
of  Wyoming  that  have  any  commercial  importance  occur  in  beds  of  the 
sedimentary  rocks.  These  clay-beds  are  most  numerous  in  the  Jurassic 
and  Cretaceous  formations,  but  are  found  to  some  extent  in  the  Tertiary." 
The  formations  containing  these  clays  are  found  flanking  nearly  all  of  the 
mountain-ranges  in  the  State,  and  the  clay-beds  vary  in  thickness  from 
4  to  40  ft.  Bowlder-clays,  that  are  so  common  in  the  East,  are  not 
known  and  will  be  found  only  in  small  and  isolated  localities.  With  the 
exception  of  the  manufacture  of  common  brick  no  attention  has  been 
paid  to  any  of  the  clay  industries,  and  all  of  the  fire-clay  goods  used  in 
Wyoming  are  manufactured  in  Colorado,  while  pressed  brick  are  shipped 
in  from  various  points.  This  condition  is  largely  due  to  the  limited  popu- 
lation of  the  State,  and  the  slight  demand  for  clay-products.  The  com- 
mon brick  which  are,  as  a  rule,  manufactured  from  loess,  are  very  siliceous 
and  fragile,  although  in  a  few  places  there  is  clay  enough  in  the  loess  to 
make  a  medium-grade  brick.  Judging  from  the  appearance  of  the  clay- 
beds  and  their  geological  position,  they  will,  when  tested,  prove  equal  to 
the  Colorado  beds. 

At  Cambria,  Weston  County,  the  clays  associated  with  the  coals  have 
been  found  adapted  to  the  manufacture  of  dry-press  brick. 

Bentonite. — A  peculiar  variety  of  clay  found  in  Wyoming  and  known 
as  bentonite  was  first  described  by  W.  C.  Knight  under  the  name  of 

1  Eng.  and  Min.  Jour.,  LXIV,  p.  546,  1898. 


458 


CLAYS 


taylorite.1  Finding  that  the  latter  name  was  preoccupied  he  proposed 
the  name  of  bentonite  for  it 2  from  its  occurrence  in  the  Benton  forma- 
tion. The  deposits  in  the  northeastern  part  of  the  State,  in  the  vicinity  of 
Newcastle,  were  first  described  in  detail  by  N.  H.  Darton.3 

Bentonite  when  fresh  has  a  yellowish-green  color,  but  assumes  a 
light  cream  tint  on  exposure.  It  is  fine-grained,  soft,  and  absorbs  three 
times  its  weight  of  water,  accompanied  by  swelling.  Its  specific  gravity 
is  2.18.  Professor  Knight  pointed  out  its  resemblance  to  the  ehren- 
bergite  of  Germany,  but  it  differs  from  it  in  containing  less  alkali.  The 
soda  reported  in  the  analyses  is,  as  a  rule,  found  in  the  clay  in  thin  seams 
as  sodium  sulphate.  The  following  analyses  were  made  at  the  Wyoming 
School  of  Mines. 

ANALYSES  OF  BENTONITE 


Peach 
Creek. 

Crook 
County. 

Weston 
County. 

Natrona 
County. 

Silica  (SiO2)  

59  78 

61    06 

63    25 

65  24 

Alumina  (A12O3). 

15  10 

17    12 

17  62 

15  88 

Ferric  oxide  (Fe2O3)  

2.40 

3  17 

3  70 

3  12 

Magnesia  (MgO)  

4  14 

1  82 

3  70 

1    5.34 

Lime  (CaO)  

0.73 

2  69 

4  12 

Soda  (Na2O)  

0  20 

Sulphur  trioxide  (SO3) 

0  80 

1  53 

Water  (H2O) 

16  26 

9  17 

Specific  gravity  .  .  . 

2  18 

2  132 

The  peculiarity  of  composition  of  this  clay  lies  in  its  high  combined 
water-content  as  compared  with  the  alumina  percentage. 

The  clay,  which  occurs  in  the  Benton  group  of  the  Cretaceous,  has  been 
found  extensively  in  Wyoming  in  Crook,  Johnson,  Weston,  Converse, 
Natrona,  Carbon,  Albany,  and  Laramie  counties.  More  recently  addi- 
tional deposits  have  been  discovered  8  miles  east  of  Frannie,  and  5 
miles  north  of  Cowley,  Wyoming.4  The  distribution  of  the  Benton 
formation  in  Wyoming  is  shown  in  Fig.  65. 

Bentonite  has  been  used  in  the  manufacture  of  soap,  as  a  packing 
for  a  special  kind  of  horseshoe,  as  a  diluent  for  certain  powerful  drugs 
sold  in  the  powdered  form,  and  as  an  adulterant  of  candy. 

xEng.  and  Min.  Jour..  LXI1I,  p.  600,  1898. 
2  Ibid.,  LXVI,  p.  491. 
8  Geologic  Atlas,  Folio  No.  107,  1904. 
4U.  S.  Geol.  Surv.,  Bull.  260,  562,  1905. 


NORTH  DAKOTA  TO  WYOMING 


459 


References  on  Wyoming  Clays 

1.  Darton,  N.  H.,  U.  S.  Geol.  Surv.,  Geol.  Atlas  Folio   107,  1904. 

2.  Fisher,  C.  A.,  The  Bentonite  Deposits  of  Wyoming,  U.  S.  Geol. 
Surv.,  Bull.  260,  p.  559,  1905. 

3.  Knight,  W.  C.,  Bentonite,  Eng.  and  Min.  Jour.,  LXIV,  p.  491, 
1898. 

4.  Knight,  W.  C.,  Wyoming  Clays  and  Building-stones,  Eng.  and 
Min.  Jour.,  LXIV,  p.  546,  1898. 

5.  Knight,  W.  C.,  Eng.  and  Min.  Jour.,  LXIII,  p.  600. 

6.  Knight,    W.  C.,  Mineral    Resources  of  Wyoming,  Wyo.  Exper. 
Sta.,  Bull.  14,  1893. 


FIG.  65. — Map  of  Benton  formation  in  Wyoming.     (After  Fisher,  U.  S.  Geol.  Surv., 

Bull.  260.) 


CHAPTER  VIII 
FULLERS'   EARTH 

Properties 

FULLERS'  earth  is  a  peculiar  type  of  clay,  which  has  the  power  of 
absorbing  greasy  substances.  In  its  appearance  when  dry  it  is  often 
difficult  to  distinguish  from  ordinary  clay,  but  when  wet  is  often  of 
lean  character.  The  statement  usually  seen  in  print  that  it  lacks 
plasticity  and  falls  to  pieces  in  water  is  misleading  and  of  no  value- 
When  dried,  fullers'  earth  often  adheres  strongly  to  the  tongue,  but  so 
do  some  ordinary  clays  which  have  no  clarifying  powers.  The  color 
is  also  variable. 

The  quantitative  analysis  shows  that  its  common  chief  difference 
from  ordinary  clay  lies  in  its  relatively  higher  percentage  of  combined 
water,  but  a  chemical  analysis  is  of  little  value,  and  a  practical  test  is 
necessary  in  order  to  determine  its  worth.  An  incorrect  statement 
often  seen  in  print  is  that  fullers'  earths  contain  a  high  magnesia-content. 

Dana1  defines  fullers'  earth  as  including  many  kinds  of  "unctuous 
clays,  gray  to  dark  green  in  color,  and  being  in  part  kaolin  and  in  part 
smectite."  It  is  placed  by  him  with  several  clay-like  minerals  (all  of 
them  hydrous  silicates),  namely,  smectite  and  malthacite,  of  not  very 
definite  chemical  composition,  but  all  having  a  high  percentage  of  com- 
bined water. 

Smectite  proper  is  defined  as  a  "mountain-green,  oil-green,  or  gray- 
green  clay,  from  Cilly  in  Lower  Styria." 

Malthacite  is  defined  as  occurring  in  thin  lamina?  or  scales,  and  some- 
times massive,  with  the  color  white  or  yellowish.  The  original  occur- 
rence is  the  result  of  disintegration  in  a  basalt  at  Steindorfel,  in  Lausitz. 
Beraum,  in  Bohemia,  is  another  locality.  It  is  not  quite  clear  on 
what  evidence  Dana  proves  fullers'  earth  to  be  a  mixture  of  "kaolin" 

1  System  of  Mineralogy,  1893,  p.  695. 

460 


FULLERS'   EARTH  461 

(he  probably  meant  kaolinite)  and  smectite,  for  the  chemical  analysis 
alone  would  not  warrant  this  statement,  and  petrographic  examina- 
tions (see  below)  afford  little  aid  in  this  matter. 

Indeed  none  of  the  published  analyses  of  fullers'  earth  show  a 
composition  at  all  similar  to  either  smectite  or  malthacite,  and  what 
their  mineral  composition  is  has  not  been  proven. 

Merrill1  states  that  "  the  English  earth,  when  examined  under  the 
microscope,  consists  of  extremely  irregular  colored  particles  of  a  sili- 
ceous mineral  which  in  its  least  altered  state  is  colorless,  but  which  in 
nearly  every  case  has  undergone  a  chloritic  or  talcose  alteration,  whereby 
the  particles  are  converted  into  a  faintly  yellowish-green  product.  The 
grains  are  of  all  sizes  up  to  .07  mm.,  but  the  larger  portion  of  the  material 
is  made  up  of  particles  fairly  uniform  in  size  and  about  the  dimensions 
mentioned.  In  addition  to  these  are  minute  colorless  fragments  down 
to  sizes  .01  mm.  and  even  smaller.  The  minute  size  of  these  colorless 
particles  renders  a  determination  of  their  mineral  nature  practically 
impossible,  but  the  outline  of  the  cleavage  flakes  is  suggestive  of  a 
soda-lime  feldspar." 

"The  Gadsden  County,  Fla.,  earth  under  the  microscope  shows  the 
same  greenish,  faintly  doubly  refracting  particles  as  does  the  English, 
Intermixed  with  numerous  angular  particles  of  quartz." 

Up  to  within  a  few  years  ago  nearly  all  of  the  fullers'  earth  used 
in  the  United  States  was  imported  from  England,  where  large  deposits 
of  this  material  exist,  but  since  that  time  deposits  have  been  found 
in  a  number  of  States,  including  Florida,  Georgia,  Alabama,  Arkansas, 
Colorado,  New  York,  South  Dakota,  and  California. 

Distribution  in  the  United  States 

But  little  has  been  published  regarding  the  American  fullers'  earth 
occurrences. 

Georgia-Florida. — Those  of  northern  Florida  and  the  adjoining 
parts  of  Georgia  were  first  described  by  H.  Ries2  and  later  by  T.  W. 
Vaughan 3  and  D.  T.  Day.4  According  to  these  writers  extensive  de- 
posits of  fullers'  earth  are  found  in  the  southern  part  of  Decatur  County, 
Ga.,  and  in  Gadsden  County,  Fla.,  in  the  western  portion  of  Leon  County, 
Fla.,  and  a  few  other  points. 

1  Guide  to  Study  of  Non-metallic  Minerals,  p.  337,  1901. 

2  U.  S.  Geol.  Surv.,  17th  Ann.  Rept.,  Pt.  Ill  (ctd.),  P-  877. 
3U.  S.  Geol.  Surv.,  Min.  Res.,  1901,  p.  922,  1903. 

4  Jour.  Frank.  Inst.,  CL,  1900. 


462  CLAYS 

According  to  Vaughan's  1  determinations  the  stratigraphic  position 
of  the  fullers'  earth,  excepting  that  from  Alachua  County,  is  Upper 
Oligocene.  The  sections  seen  in  the  pits  vary  at  the  different  localities, 
but  the  following  might  serve  as  representative. 

Feet. 

Overburden  (Sandy  clay) 5  to  20 

Fullers'  earth 6  to   10 

Sandstone  with  crystals  and  lumps  of  calcite  or  aragonite ...   3  to     4 
Fullers'  earth 5  to     6 

Most  of  the  earth  when  dry  is  of  whitish  color,  flaky,  brittle,  and 
adheres  strongly  to  the  tongue.  Analyses  are  given  below,  and  a  view 
of  one  of  the  pits  is  shown  in  PL  XLIV,  Fig.  1. 

South  Carolina,  North  Carolina,  and  Virginia. — Earth  of  very  fair 
quality  has  been  obtained  from  near  Sumter,  South  Carolina,  and  deposits 
are  also  known  in  North  Carolina  and  Virginia,  but  the  earth  from  the 
last  two  is  more  or  less  sandy.2 

New  York. — In  this  State  deposits  of  fullers'  earth  occur  at  McCon- 
nellsville,  12  miles  north  of  Rome.  The  material  is  a  fine-grained,  dense, 
Quaternary  clay  in  layers  2  to  8  inches  thick,  interbedded  with  layers  of 
sand  of  similar  thickness.  This  earth  has  been  used  only  for  cleansing 
woolen  goods.3 

Arkansas. — Deposits  of  earth  are  worked  in  Arkansas,  and  analyses 
of  some  fullers'  earth  from  that  State  are  given  in  the  table  below. 

South  Dakota. — In  South  Dakota  4  the  first  deposits  were  located 
and  opened  up  five  miles  southeast  of  Fairburn,  Custer  County,  the 
section  showing: 

Feet. 

Micaceous  sandy  clay 6 

Fullers'  earth 9 

Micaceous  sandstone 

The  earth  is  a  yellowish  gritty  clay,  with  a  somewhat  nudular  structure. 
Other  deposits  are  known  near  Argyle  and  Minnekata.  The  deposits 
are  of  Jurassic  age. 

California. — Fullers'  earth  is  said  to  occur  in  Kern  and  San  Ber- 
nardino counties,  but  only  that  in  the  former  appears  to  have  been 

1  L.  c.,  p.  923. 

2  Day,  1.  c.,  p.  591. 

,   3  N.  Y.  State  Mus.,  Bull.  35,  850,  1900. 

4  H.  Ri«g,  Amer.  Inst.  Min.  Eng.,  Trans.,  XXVII,  p.  333,  1898. 


PLATE  XLIV 


FIG.   1.— Fullers'-earth  pit,  Quincy,  Fla.     Behind  it  are  the  drying-floors. 
(Photo  by  H.  Ries.) 


FIG.  2. — Outcrop  of  fullers'  earth,  northeast  of  Fairburn,  S.  Dak. 
(After  Todd,  S.  Dak.  Geol.  Surv.,  Bull.  3,  p.  121,  1902.) 

463 


FULLERS'   EARTH 


465 


worked.1     It  is  said  to  range  from  15  to  50  feet  in  thickness.     The 
deposits  are  of  Cretaceous,  Tertiary,  and  Pleistocene  age. 

The  following  table  gives  the  composition  of  fullers'  earth  from  a 
number  of  different  localities: 

ANALYSES  OF  FULLERS'  EARTH 


I. 

II. 

III. 

IV. 

V. 

Silica  (SiO-0 

51.21 
12.25 
2.07 
2.13 
4.89 

50.17 
10.00 
9.75 
0.50 
1.25 

47.10 
16.27 
10.00 
2.63 
3.15 

62.83 
10.35 
2.45 
2.43 
3.12 
0.74 
0.20 
7.72 
6.41 

67.46 
10.08 
2.49 
3.14 
4.09 

5.61 

6.28 

Alumina  (AlgOs) 

Ferric  oxide  (FeoOs) 

Lime  (CaO) 

Magnesia  (MgO).  . 

Potash  (K2O)                

Soda  (Na2O)                  .    .    . 

Water  (HaO)   

27.89 

24.00 

15.12 
5.73 

Moisture   ...         

Loss  on  ignition  

• 

Total  

100.41 

100.06 

100.00 

96.25 

99.15 

VI. 

VII. 

VIII. 

IX. 

X. 

Silica  (SiOv)  

58.72 
16.90 
4.00 
4.06 
2.56 

}  ,n 

8.10 
2.30 

50.36 
33.38 
3.31 

74.90 
10.25 
•  1.75 
1.30 
2.30 

1.75 

5.80 
1.70 

54.32 

18.88 
6.50 
1.00 
3.22 

4.21  | 
11.86 

63.19 
18.76 
7.05 
0.78 
1.68 
0.21 
1.50 
7.57 

Alumina  (A12O3)  
Ferric  oxide  (Fe^Os) 

Lime  (CaO) 

Magnesia  (MgO)  
Potash  (K.O).           .    . 



SnHfl    (Na  O"i 

Water  (H2O).  

12.05 

Moisture  

Loss  on  ignition  

Total  '  
1 

. 

98.45 

99.10 

99.75 

99.99 

100.74 

I    Smectite  from  Cilly.     Pogg.  Ann.,  LXXVII,  p.  591,  1849. 
II.   Malthacite  from  Steindorfel.     Dana,  Syst.  Min.,  1893. 

III.  Woburn  sands,  Eng.  (yellow),  R.  H.  Harland,  anal. 

IV.  Gadsden  County,  Fla.,   P.  Fireman,  anal.      U.  S.  Geol.  Surv.,  17th  Ann.  Kept.,  Pt.  Ill 

(ctd.),  p.  880. 

V    Decatur  County,  Ga.,  ibid. 
VI.   Fairburn,  S.  Dak.,  E.  J.  Riederer,  anal.      U.  S.  Geol.  Surv.,  17th  Ann.  Rept.,  Pt.  Ill  (ctd.), 

p.  880. 

VII.  Glacialite,  Enid,  Okla,  Ter.     G.  P.  Merrill,  Non-metallic  Minerals. 
VIII.   Sumter,  S.  Ca.,  H.  Ries,  anal.     U.  S.  Geol.  Surv.,  Min.  Res.,  1901,  p.  932,  1902. 
IX.   Bakersfield,  Kern  County,  Calif.     Min.  Indus.,  X,  p.  273. 

X.  Alexander,  Ark.,  1  S.,  13  W.,  Sec.  8,  S.  W.  i  of  S.  E.  |.     Branner,  Amer.  Inst.  Min.  Eng., 
Trans.,  XXVII,  p.  62,  1898. 


>  Calif.  State  Min.  Bur.,  Bull.  38,  p.  274,  1906. 


466  CLAYS 


Mining  and  Uses 

According  to  Ries  l  "The  Florida  earth  is  usually  mined  with  picks 
and  shovels."  A  good  method  is  to  use  mattocks,  which  shave  the  mate- 
rial off  in  thin  pieces,  and  saves  subsequent  labor  in  breaking  up  the 
fullers'  earth  after  it  has  been  spread  upon  the  drying-floor.  After 
mining  the  usual  method  is  to  spread  the  material  in  a  thin  layer  over  a 
drying-floor  constructed  of  planks.  It  is  thus  dried  in  the  sun,  and  in 
drying  it  bleaches  to  a  white  color.  The  material  is  then  gathered  into 
sacks  for  shipment.  By  this  air-drying  about  50  per  cent  of  moisture  is 
removed.  Drying  can  be  done  more  rapidly  by  passing  the  earth  through 
a  hot  cylinder. 

Day  2  states  the  following  regarding  the  uses  of  fullers'  earth : 

"The  Florida  earth,  ground  to  60  mesh  and  finer,  is  used  almost  exclu- 
sively as  a  substitute  for  bone-black  in  filtering  mineral  lubricating-oils, 
although  its  use  has  been  somewhat  extended  for  the  lightening  of  the 
color  of  cottonseed-oil,  but  for  this  latter  purpose  the  employment  of. 
English  fullers'  earth  is  still  generally  practiced.  The  English  earth 
has  not  proved  any  more  suitable  for  the  refining  of  mineral  oils  than 
has  the  American  earth  for  use  in  vegetable  oils.  The  common  practice 
with  these  mineral  oils  is  to  dry  the  earth  carefully,  after  it  has  been 
ground  to  60  mesh,  and  run  it  into  long  cylinders,  through  which  the 
crude  black  mineral  oils  are  percolated  very  slowly.  As  a  resul:  the 
first  oil  which  comes  out  is  perfectly  water  white  in  color,  and  markedly 
thinner  than  that  which  follows.  The  oil  is  allowed  to  continue  perco- 
lating through  the  fullers'  earth  until  the  color  reaches  a  certain  maxi- 
mum shade,  when  the  process  is  stopped,  to  be  continued  with  a  new 
portion  of  earth.  The  oil  is  recovered  from  the  spent  earth. 

"  With  the  vegetable  oils  the  process  is  radically  different.  The  oil 
is  heated  to  beyond  the  boiling-point  of  water  in  large  tanks,  and  from 
5  to  10  per  cent  of  its  weight  of  fullers'  earth,  ground  to  100  or  120  mesh, 
is  then  added,  and  the  mixture  vigorously  stirred  for  20  minutes,  and 
then  filtered  through  the  bag  filters.  The  coloring-matter  remains  in 
the  earth,  leaving  the  oil  of  a  very  pale  straw  color,  provided  the  original 
cottonseed-oil  had  been  sufficiently  well  refined  by  the  ordinary  process 
to  admit  of  this,  and  provided  the  operation  had  been  conducted  with 
sufficient  care." 

1  L.  c.,  p.  879. 

2  U.  S.  Geol.  Surv.,  21st  Ann.  Kept.,  Pt.  6  (ctd.),  P-  592. 


FULLERS'  EARTH  467 

Fullers'  earth  was  originally  used  for  fulling  cloth,  that  is,  cleansing  it 
of  grease,  but  this  is  now  its  least  important  application.  It  is  also 
employed  in  the  manufacture  of  certain  soaps.  Its  use  for  removing 
calcium  carbonate  from  water  for  boiler-supply,  thus  preventing  dele- 
terious incrustations,  is  also  suggested.1 

Production. — The  total  production  of  fullers'  earth  for  1904  is 
given  by  the  U.  S.  Geological  Survey  as  29,480  short  tons  valued  at 
$168,500,  the  greater  part  of  the  supply  coming  from  Florida,  and  the 
balance  from  Arkansas,  Alabama,  Massachusetts,  Colorado,  and  New 
York. 

The  total  imports  of  both  prepared  and  crude  earth  in  1904  amounted 
to  9126  long  tons  valued  at  $74,006. 

1  U.  S.  Geol.  Surv.,  Min.  Res.  for  1904,  p.  1121,  1905. 


INDEX 


A 


Aarons,  cited,  99,  101 
Abbotsford,  Wis.,  452 
Acetates,  adsorption  of,  164 
Adobe,  analyses  of,  187 

New  Mexico,  373 
Adsorption,  163 
^Eolian  clays,  23 

Agar-agar,  effect  on  plasticity,  102 
Affelder,  cited,  411 
Aiken,  S.  C.,  415,  416 
Air-separators,  214 
Air  shrinkage,  128 

cause  of,  128 

range  of,  128 
Akron,  Ohio,  392,  393 
Alabama,  clays  described,  283 

mentioned,  179,  278 

Pleistocene  clays,  284 

Tertiary  clays,  283 
Albany  clay.     See  Slip-day 
Albany  County,  Wyo.,  458 
Albite,  adsorptive  power,  164 

kaolinization,  3 

solubility,  2 
Aleksiejew,  cited,  98 
Alexander  County,  111.,  304 
Alexandria,  Va.,  437 
Alfred  Centre,  N.  Y.,  378 
Algonkian,  198,  278,  334 
Alkalies,  determination  of,  64 

effect  on  clay,  82 

fixed,  82 

Allegany  County,  Md.,  335 
Allegheny  County,  407,  411 

series,  336,  394,  405,  445 
Allophane,  dehydration  temperature,  52 

mentioned,  309 

properties  of,  51 
Alloway  clay,  N.  J.,  370,  371 
Alluvial  clays,  Oklahoma,  400 

South  Dakota,  420 

Tennessee,  423 

Texas,  431 


Alpena,  Mich.,  345 

Alton  clay,  Pa.,  402 

Alum,  389 

Alumina,  adsorption  of,  by  clay,  163 

as  coloring  agent  in  clay,  159,  162 

determination  of,  65 

effect  on  iron  coloration,  73 
Alumina  cream,  effect  on  plasticity,  101. 

102 

Amboy  stone  ware- clay,  369 
Anadarko,  Okla.,  400 
Analcite,  as  source  of  kaolinite,  47 
Analyses  of,  adobe  soils,  187 

Alabama  clays,  284 

Arkansas  clays,  286 

ball-clays,  169 

bentonite,  458 

brick-clays,  common,  185 

calcareous  clays,  78 

clay  types,  60 

Colorado  clays,  293 

Connecticut  clays,  296 

different  layers  in  bank,  60 

fire-clays,  178 

fire -proofing  clay,  193 

Florida  clays,  298 

fullers'  earth,  465 

Georgia  clays,  303 

halloysite,  49 

Indiana  clays,  314 

indianaite,  50 

Iowa  clays,  325 

kaolins,  168 

Kentucky  clays,  330 

loess,  187 

Maryland  clays,  338 

Massachusetts  clays,  341 
kaolins,  340 

mechanical  separations,  118 

Michigan  clay,  346,  347 

Minnesota  clays,  351 

Missouri  clays,  361 

New  Jersey  clays,  372 
fire  clays,  175 

New  York  clays,  381 


470 


INDEX 


Analyses  of  North  Carolina  clays,  386 

North  Dakota  clay,  390 

Ohio  clays,  398,  399 

Pennsylvania  clays,  413 

Portland -cement  clay,  198 

pressed  brick  clays,  188 

residual  clays,  13 

sewer-pipe  clays,  183 

slip-clays,  195 

South  Carolina  clays,  416 

South  Dakota  clays,  420 

stoneware-clays,  181 

Tennessee  clays,  424 

Texas  clays,  431 

Vermont  kaolins,  334 

Virginia  clays,  438 

West  Virginia  clays,  449,  450 

Wisconsin  clays,  456 
Analysis  of  albite,  3 

altered  feldspar,  4,  5 

anorthite,  3 

clay,  Ferguson,  Okla.,  400 

Cornwall  stone,  11 

glauconite,  57 

fire-clay,  Mexico,  Mo.,  359 
Ohio,  190 
St.  Louis,  Mo.,  356 

halloysite,  49,  50 

hydrous  silica,  70 

indianaite,  310 

kaolin,  4,  11 

kaolinite,  50 
artificial,  5 

labradorite,  4 

non-magnesian  clay,  81 

orthoclase,  3,  5 

shale,  Mo.,  359 

See  Rational  analysis,  Ultimate  analy- 
sis 

Andalusite,  as  source  of  kaolinite,  47 
Anderson  Station,  Tenn.,  421 
Anglesey,  kaolinite  crystals,  42 
Angola,  N.  Y.,  376 
Anne  Arundel  County,  Md.,  336,  337 
Anorthite,  kaolinization  of,  3 
Anorthoclase,  as  source  of  kaolinite,  47 
Anticlines,  28 

Appalachians,  residual  clays  in,  12 
Aragonite,  426 
Archaean  clays,  278 
Arenac  County,  Mich.,  345 
Argyle,  S.  Dak.,  fullers'  earth  at,  462 
Arizona,  clays  of,  286 
Arkansas,  Carboniferous  shales,  285 

clays  described,  285 

fullers'  earth,  462 

kaolin,  285 

mentioned,  179 

Mesozoic  clays,  285 

Pleistocene  clays,  285 
Armstrong  County,  Pa.,  407,  411 
Art  ware,  182 


Arundel  formation,  337 

Asbury  clay,  370 

Asbury  Park,  N.  J.,  127 

Ashley,  cited,  311 

Atchison,  Kan.,  326 

Athens,  Tex.,  181,  431 

Athens  County,  Ohio,  398 

Atlantic  coast  plain,  dip  of  clay- beds,  28 

Attica,  Ind.,  309 

Auger  machine,  228 

Augite,  4,  41 

Augusta,  Ga.,  301,  416 

Augusta  shales,  la.,  318 

Aurora,  Mo.,  354 

halloysite  at,  49 
Austin,  Tex.,  431 
Austin  chalk,  Tex.,  427 


B 


Bacteria,  effect  on  plasticity,  104 
Ball-clay,  chemical  composition,  169 

distribution,  169 

Florida,  169,  297 

Kentucky,  329 

mentioned,  214,  271,  257 

Missouri,  355 

New  Jersey,  169 

properties  of,  168,  169 

Tennessee,  423 
Ball-mills,  described,  265 
Baltimore  County,  Md.,  336,  337 
Barbour,  E.  H.,  cited,  362 
Barium,  adsorption  by  clay,  163 
Barlow,  W.  Va.,  446 
Barringer,  cited,  81 
Barrington,  R.  I.,  415 
Basalt,  as  source  of  malthacite,  460 
Bath  brick,  199 
Bath-tubs,  manufacture  of,  276 
Baton  Rouge,  La.,  331 
Bauxite,  51,  167 
Bay  City,  Mich.,  345 
Beattystown,  N.  J.,  364 
Beaumont,  Tex.,  431 
Beaumont  clays,  Tex.,  431 
Beaver  County,  Okla.,  400 
Beaver  County,  Penn.,  405,  407,  411 
Beaver  River  region,  Pa.,  405, 407,  408,  413 
Bedford,  Ohio,  392 
Bedford  shale,  392 
Bell,  cited,  2 
Bellaire,  Ohio,  398 
Belmont,  Mass.,  341 
Belmont  County,  Ohio,  398 
Benezette,  Pa.,  406 
Bennington,  Vt.,  333 
Ben's  Run,  Pa.,  406 
Ben  ton  County,  Ind.,  313 
Ben  ton  group,  389,  458 
Bentonite,  described,  457,  458 


INDEX 


471 


Bentonite,  uses  of,  458 
Berdel,  cited,  83 
Berkeley  County,  W.  Va.,  442 
Berlin,  Conn.,  295 
Bermuda  Hundred,  Va.,  437 
Beryl,  kaolinization  of,  4 
Beverly,  Mass.,  342 
Beyer,  S.  W.,  cited,  123,  127,  137,  318 
Bibbville,  Ala.,  283 
Biedermann,  cited,  98 
Big  Stone  City,  S.  Dak.,  420 
Biotite,  as  source  of  kaolinite,  47 
mentioned,  41,  71,  131 
occurrence  in  clay,  54 
Birmingham  shale,  W.  Va.,  446 
Bfachof,  cited,  101,  145 
Bismarck,  N.  Dak.,  390 
Bituminous  matter,  Texas  clay,  427 
Black  coring,  90 
Black  Lick,  Pa.,  406 
Black  River  Falls,  Wis.,  452 
Blair  County,  Pa.,  407 
Blake,  cited,  48,  51,  97 
Blandford,  Mass.,  340 
Bleininger,  A.  V.,  cited,  190 
Block  House  Run,  Pa.,  411 
Blue  Ball,  Pa.,  406 
Bluff  deposit,  Neb.,  363 
Bolivar,  Pa.,  411 
Bollinger  County,  Mo.,  354= 
Bordentown,  N.  J.,  370 
Boring  methods,  203 
Bostick's  Mills,  N.  C.,  385 
Boston,  Mass.,  341 
Boulder,  Colo.,  290 
Bourry,  cited,  163 
Bowlder-clays,  20 
Boyd  County,  Ky.,  329 
Brady's  Run,  Pa.,  406 
Brandon,  Vt.,  333 
Brandy  wine  Summit,  Pa.,  402 
Brick,  common,  denned,  218 

enameled,  denned,  218 

front,  denned,  218 

glazed,  denned,  218 

manufacture  of,  218 

soft- mud,  characteristics  of,  227 

stiff-mud,  characteristics  of,  228 
Brick-clay,  adobe,  186 

Alabama,  283 

Arizona,  286 

Arkansas,  285 

California,  286,  289 

Colorado,  290 

common,  analyses  of,  185 
physical  tests  of,  186 
properties  of,  185 

Connecticut,  295 

District  of  Columbia,  296 

enameled,  191 

Florida,  297 

Illinois,  304 


Brick-clay,  Indiana,  307,  309,  313 

Indian  Territory,  315 

Iowa,  316,  318,  322 

Kentucky,  328 

Maryland,  335,  338 

Massachusetts,  341 

Michigan,  345 

Minnesota,  348 

Missouri,  359 

Nebraska,  363 

New  Mexico,  373 

New  Jersey,  364,  371 

New  York,  378 

North  Carolina,  385,  386 

North  Dakota,  390 

Ohio,  392 

Oklahoma,  400 

Pennsylvania,  402,  413 

pressed,  analyses  of,  188 
flashing  of,  189 
physical  tests,  188,  189 
properties  of,  188 

Rhode  Island,  415 

Tennessee,  421 

tensile  strength,  122 

Texas,  426,  427,  428,  431 

Utah,  434 

Virginia,  434,  437 

Washington,  441 

West  Virginia,  442,  445,  446 

Wisconsin,  452,  455,  456 

Wyoming,  457 
Brick-manufacture,  burning,  236 

drying,  232 

molding,  220 

preparation,  218 
Bridgeboro,  N.  J.,  370 
Bridgeport,  Tex.,  426 
Bridgeton,  N.  J.,  371 
Briquettes,  tensile  strength,  120 
Bronson,  Mich.,  346 
Brookville,  Pa.,  406 
Brookville  clay,  394,  395,  405 
Bryson  City,  N.  C.,  385 
Buchanan  County,  Iowa,  318 
Buckley,  cited,  25,  41,  455 
Buffalo,  N.  Y.,  378 
Burlington,  N.  J.,  370 
Burlington  shale,  Mo.,  355 
Burning  clay,  changes  occurring  in,  156 

dehydration  period,  157 

oxidation  period,  158 

volatilization  during,  160,  161 

vitrification  period,  159 
Butler  County,  Pa.,  402 


Cairo,  N.  Y.,  376 
Calcareous  clays,  Texas,  431 

Wisconsin,  455 

Michigan,  344 


472 


INDEX 


Calcite,  41,  55,  76,  98,  136 
Calhoun,  Mo.,  181 
Calhoun  County,  Iowa,  321 
California,  clays  described,  286 

fullers'  earth  in,  462 

references  on,  289 

Tertiary  clays,  289 
Calumet  County,  Wis.,  455 
Cambria,  Wyo.,  457 
Cambrian  clays,  283,  316,  354,  355 
Cambridge,  Mass.,  341 
Cambridge  limestone,  West  Virginia,  446 
Cambro-Silurian,  198,  434 
Camden,  N.  J.,  370 
Camden,  S.  C.,  415,  416 
Cameron,  cited,  2 
Cameron  County,  Pa.,  402 
Cancrinite,  solubility  of,  2 
Cannel,  Tex.,  428 
Canton,  Ohio,  395,  396 
Canton,  N.  C.,  385 
Cape  Girardeau  County,  Mo.,  354 
Cape  May  formation,  N.  J.,  371 
Carbon,  asphaltic,  88 

effects  on  clay,  88 
Carbon  County,  Pa.,  402 
Carbon  County,  Wyo.,  458 
Carbonaceous  clay,  Tex.,  426 
Carbonaceous   matter,   as  coloring  agent, 

161.     See  Carbon 
Carbondale,  Cal ,  289 

Carbon  dioxide,  relating  to  weathering,  2,  4 
Carboniferous  clays,  Indiana,  309 

Iowa,  318 

Kansas,  326 

Kentucky,  328 

Maryland,  335 

mentioned,  39,  55,  178,  179,  183,  185, 
191,  192 

Michigan,  345 

Mississippi,  352 

Missouri,  356 

Pennsylvania,  402 

Tennessee,  421 

Texas,  426 

Virginia,  437 

West  Virginia,  442 
Carboniferous  shales,  siderite  in,  55 
Carclazite,  211 
Carlisle  shale,  Colo.,  290 
Carroll  County,  Ohio,  396 
Carter  County,  Ky.,  329 
Cassville  coal,  398 
Casting  pottery,  269 
Catskill  shale,  W.  Va.,  442 
Cecil  County,  Md.,  334,  336,  337 
Cedar  County,  Iowa,  318 
Ceredo,  W.  Va.,  446 
Chagrin  shale,  Ohio,  392 
Chamberlin,  T.  C.,  cited,  41 
Champlain  Valley,  N.  Y.,  378 
Chandler,  Okla.,  400 


Chanute,  Kan.,  326 
Charlestown,  W.  Va.,  442,  446 
Chaser-mills,  240,  265 
Chemical  analysis  of  clays,  58 
Chemical  changes  in  clays,  33 
Chemical  composition,  relation  to  fusibil- 
ity, 139 

Chemical  properties  of  clays,  40 
Chemung  shale,  New  York,  376 

West  Virginia,  442 
Cheraw,  S.  C.,  416 
Cherryvale,  Kan.,  326 
Chert,  52 

Chester,  Minn.,  351 
Chester  County,  Pa.,  401 
Chesterfield,  S.  C.,  415 
Chicago,  111.,  304 
China  clay.     See  Kaolin 
Chittenden,  Vt.,  333 
Chlorides,  adsorption  by  clay,  164 
Chlorite,  41 

Chromolithography,  275 
Cilly,  Styria,  460 
Cimolite,  51 
Cincinnati  shales,  304 
Cisco,  Tex.,  426 
Clarion  clay,  406,  445 
Clarke  County,  Wis.,  452 
Clay,  absorption  of  water  by,  86 

adobe,  186 

adsorptive  power,  163 

aeolian,  23 

air-separation  of,  214 

air-shrinkage,  128 

alkalies  in,  82 

ammonia  in,  82 

analyses  of,  60 

ball,  168 

biotite  in,  54 

bowlder,  20 

brick,  185 

calcareous,  78 

calcareous,  uses  of,  78 

calcite  in,  55 

carbon  in,  effect  of,  88 

carbonates  in,  1 

changes  in  burning  of,  156 

chemical  analysis  of,  58 

chemically  combined  water  in,  87 

chemical  properties  of,  40 

chemical  variation  in,  60 

classification  of,  23 

colluvial,  27 

color  of,  160,  161 

delta,  25 

definition  of,  1 

dolomite  in,  57 

drift,  20 

enameled  brick,  191 

estuarine,  19 

feldspar  in,  53 

fire,  170 


INDEX 


473 


Clay,  fireproofing,  192 
fire-shrinkage,  129 
flood*plain,  20 
fusibility  of,  137 
garnet  in,  57 
glacial,  20,  360 
glass-pot,  196 
glauconite  in,  57 
gumbo,  195 
gypsum  in,  56,  78 
hematite  in,  54 
hollow-brick,  192 
hornblende  in,  57 
hydrous  silica  in,  70 
hydroxides  in,  1 
i  menite  in,  56 
iron  compounds  in,  72 
iron  in,  coloring  action  of,  72 
iron  oxides  in,  54,  71 
kaolin,  165 
kinds  of,  165 
lake,  20 
lepidolite  in,  54 
lime  in,  76 
lime  carbonate  in,  76 
lime  silicates  in,  78 
limonite  in,  54 
littoral,  25 
loess,  186,  360 
magnesia  in,  80 
magnesite  in,  57 
magnetite  in,  55 
manganese  in,  58 
manufacturing  methods,  217 
marine,  19 

mechanical  analysis  of,  108 
meta-ssdimentary,  25 
mica  in,  53 

mineral  compounds  in,  68 
minerals  in,  40 
mining  methods,  204 
miscellaneous  kinds  of,  195 
moisture  in,  86 
mottling  of,  34 
muscovite  in,  54 
origin  of,  1 
outcrops,  199 
oxides  in,  1 
paint,  198 
paper,  197 
parent  rock  of,  1 
paving-brick,  191 
pelagic,  25 
permeability,  163 
physical  properties  of,  94 
pipe,  196 
plasticity  of,  94 
polishing,  199 
Portland  cement,  197 
potash  in,  82 
preparation  of,  213 
pressed  brick,  187 


Clay,  prospecting  for,  199 

pure,  8 
•pyrite  in,  55 

quartz  in,  52 

rare  elements  in,  58 

rational  analysis  of,  61 

residual,  11 

rutile  in,  56 

sagger,  196 

secondary  character  of,  1 

sedimentary,  14 

selenite  in,  56 

sewer-pipe,  183 

siderite  in,  55 

silica  in,  68 

silicates  in,  1 

slip,  193 

soda  in,  82 

soluble  salts  in,  90 

specific  gravity  of,  136 

statistics,  288 

stoneware,  180 

swamp,  20 

tensile  strength  of,  120 

terra-cotta,  182 

texture  of,  108- 

titanium  in,  84 

transported,  14 

tourmaline  in,  57 

ultimate  analysis  of,  58 

ultramarine,  199 

uses  of,  217 

vanadiates  in,  57 

vivianite  in,  58 

wad,  197 

ware,  196 

washing,  213  "" 

water  in,  86 

weathering  of,  104 
Clay- deposits,  change  of  color,  35 

chemical  changes  in,  33 

classification  of,  23 

concretions  in,  35 

consolidation  of,  35 

discoloration  of,  34 

erosion  of,  30 

exploitation  of,  203 

faulting  of,  28 

folding  of,  28 

leaching  of,  35 

mechanical  changes  in,  28 

secondary  changes  in,  28 

softening  of,  35 

tilting  of,  28 
Clay  Marl  series,  370 
Clay-mining,  212 
Clay-products,  statistics,  278 
Clay -slides,  205 
Clay  substance,  5 
Clayton,  Mass.,  340 
Clayton,  Wash.,  441 
Cleveland,  Ohio,  392 


474 


INDEX 


Cleveland  shales,  Ohio,  392 
Cliffwood  clays,  New  Jersey,  369 
Clinton  shale,  New  York,  376 

Pennsylvania,  402 

West  Virginia,  442 
Cloverport,  Ky.,  329 
Coal,  Wyoming,  clays  with,  457 
Coal-measures,  303,  321,  329,  356,  393 
Coffeyville,  Kan.,  326 
Cohansey  clay,  New  Jersey,  370,  371 
Cold  water,  Mich.,  346 
Coldwater  shales,  346 
Collier,  W.  Va.,  446 
Collins,  cited,  5,  210 
Colloids,  1,  99 
Colluvial  clays,  27 
Collyrite,  51 
Color  of  clays,  161 
Colorado,  clays  described,  289 

mentioned,  179,  191 

Mesozoic  clays,  290 

Pleistocene  clays,  290 

references  on,  290 
Columbia,  S.  C.,  415,  416 
Columbian  formations,  296,  331,  337,  413, 

415,  437 

Columbiana  County,  Ohio,  396 
Columbus,  Ga.,  301 
Columbus,  Ohio,  392 
Common  brick,  185 
Concho  County,  Tex.,  426 
Concretions  in  clay,  35,  36,  427 

limonite,  54 

siderite,  55 

Conduit  clay,  New  York,  376 
Conduits,  manufacture  of,  251 

mentioned,  179,  251 
Conemaugh  series,  336,  398,  411,  446 
Cones,  Seger,  148 
Connecticut,  clays  described,  293 

Pleistocene  clays,  295 

references  on,  296 

Conoquenessing  sandstone,  Ohio,  393,  394 
Converse,  Wyo.,  458 
Cooper,  Tex.,  428 
Cook,  G.  H.,  cited,  51,  98,  104 
Cooper  County,  Mo.,  354 
Copper,  adsorption  by  clay,  164 
Copper  Queen  mine,  clay  in,  286 
Corning,  N.  Y.,  376 
Cornwall,  England,  kaolin  at,  5 
Cornwall  stone,  analysis  of,  11 
Corona,  CaL,  289 
Corsicana,  Tex.,  428 
Corunna,  Mich.,  345 
Corundum-wheels,  clay  in,  199 
Coshocton  County,  Ohio,  395 
Cowley,  Wyo.,  458 
Cox,  E.  T.,  cited,  310 
Cramer,  cited,  85,  141,  148 
Crawfordsville,  Ind.,  309 
Cremiatschenski,  cited,  98 


C.  C.  ware,  defined,  262 
Cretaceous  clays,  Iowa,  321 

Kansas,  327 

Maryland,  336 

mentioned,  28,  41,  57,  161,  169,  179, 
183,  185,  191,  197,  289,  301 

Minnesota,  348 

Mississippi,  352 

Missouri,  355 

Nebraska,  363 

New  Jersey,  366 

New  York,  378 

North  Dakota,  389 

sedimentary  clays  of,  17 

South  Dakota,  419 

Texas,  426 

Wyoming,  457 

Cretaceous  fullers'  earth,  465 
Cripple  Creek,  Colo.,  kaolin  at,  6 
Cross,  W.,  cited,  6 
Crook  County,  Wyo.,  458 
Crucibles,  179 
Crushers,  described,  219 
Cromwell,  Conn.,  295 
Cumberland  City,  Tenn.,  421 
Cumberland  County,  Pa.,  402 
Currier,  Tenn.,  423 
Cushman,  A.  S.,  cited,  101,  103,  104 
Custer,  S.  Dak.,  419 
Cyanite,  as  source  of  kaolinite,  47 


D 


Dakota  group,  290,  321,  400,  419 

Dallas,  Tex.,  427 

Dana,  E.  S.,  cited,  48,  50,  460 

Danversport,  Mass.,  342 

Darlington  clay,  407 

Darton,  N.  H.,  cited,  296,  458 

Daubree,  cited,  6,  97 

Day,  D.  T.,  cited,  461,  466 

Decatur  County,  Ga.,  461 

Delage,  cited,  41 

Delaware,  clays  described,  296 

mentioned,  198 
Delaware  County,  Pa.,  401 
Dellslow,  W.  Va.,  446 
Delta-clays,  25 
Demond,  cited,  155 
Denton,  Tex.,  427 
Denver  Basin,  clays  of,  290 
De  Smet,  S.  Dak.,  420 
Detroit,  Mich.,  346 
Devonian  shales  or  clays,  Iowa,  318 

Kentucky,  328 

Maryland,  325 

mentioned,  28,  179,  185,  191 

Michigan,  345 

Mississippi,  352 

Ohio,  392 

Pennsylvania,  402 

West  Virginia,  442 


INDEX 


475 


Diatomaceous  earth,  Virginia,  437 
Dick,  cited,  42 
Dickinson,  N.  Dak.,  389 
Discoloration  by  vanadiates,  57 
Disintegrators,  described,  219 

mentioned,  251,  252 
District  of  Columbia,  clays  of,  296 
Dolomite,  mentioned,  41,  76 

occurrence  in  clay,  57 
Dorsey,  Md.,335 
Double  coal  brick,  239 
Down-draft  kilns,  253 
Drain-tile  clay,  Connecticut,  295 

Iowa,  321 

Kansas,  326 

Missouri,  359 

New  Jersey,  371 

New  York,  376,  378 

North  Carolina,  385 

Ohio,  391,  392 
Drain-tile  manufacture,  247 
Dreux,  clay  from,  48 
Drift-clays,  20 
Drying-floors,  251 
Drying -tunnels,  described,  232 

mentioned,  252,  270 
Dry  pans,  described,  219 

mentioned,  240,  251,  252,  257 
Dry-press  brick,  290 

process,  described,  231 

mentioned,  252,  262 
Dunkard  series,  398,  449 
Durand,  Wis.,  452 
Dutch  kilns,  239 


E 


Eagle  Ford  formation,  Tex.,  427 
Eagle  Pass,  Tex.,  427,  428 
Earthenware,  denned,  262 

mentioned,  182 

red,  burning  of,  270 
Earthen  ware -clay,  Connecticut,  295 

Iowa,  316,  318 

Massachusetts,  342 

Michigan,  345 

Pennsylvania,  413 
East  Liverpool,  Ohio,  407 
Eau  Claire,  Wis.,  452 
Eden  shale,  Ohio,  391 
Edgar,  Fla.,  96,  297 
Edwards  County,  Tex.,  426 
Edwards  limestone,  kaolin  in,  426 
Ehrenbergite,    compared    with    bentonite, 

458 

Elgin,  Tex.,  431 
Elk  County,  Pa.,  402 
Elkins,  W.'  Va.,  442 
Ellerslie,  Md.,  335 
Elmendorff,  Tex.,  431 
Elmira,  N.  Y.,  378 
El  Reno,  Okla.,  400 


Elsinore,  Cal.,  289 
Enameled -brick  clays,  191 
Encaustic  tile,  258 
Eocene,  57,  352,  416,  437 
coals,  clay  with,  428 
Epidote  as  source  of  kaolinite,  47 
Erosion  of  clays,  30 
Escanaba,  Mich.,  346 
Essex  County,  Mass.,  340 
Estuarine  clays,  19,  371,  378,  455 
Excavation,  methods  of,  204 


F 


Fair  burn,  S.  Dak.,  462 
Fargo,  N.  Dak.,  390 
Farrandsville,  Pa.,  406 
Faulting  in  clay-deposits,  28 
Fayence,  architectural,  254 

denned,  262 

Fayette  County,  Pa.,  406,  407 
Fayetteville,  Pa.,  385 
Feldspar,  adsorptive  power,  163 

composition  of,  53 

mentioned,  6,  11,  41,  47,  48,  53,  68, 
70,  76,  77,  83,  84, 136, 257, 261,  275, 
385 

occurrence  in  clay,  53 

reactions  in  kaolinization  of,  47 
Feldspar  beds,  New  Jersey,  369 
Fernbank,  Ala.,  283 
Ferric  oxide,   determination  of,   65.     See 

Iron  oxide 

Ferriferous  coal  under-clay,  406 
Ferriferous  limestone-clay,  394,  395 
Ferris,  Tex.,  428 

Ferrous  oxide,  determination  of,  66 
Feuerfestigkeits-Quotient,  145 
Filter-press,  214,  264,  265 
Fire-brick,  cone  of  firing,  253 

Colorado,  290 

Connecticut,  295 

manufacture  of,  252 

requirements  of,  253 

shapes  of,  253 

texture,  253 

Weber's  experiments,  253 
Fire-clay,  Alabama,  283 

association  with  coal,  179 

chemical  composition,  170 

Colorado,  290 

definition  of,  170 

Delaware,  296 

distribution,  geographic,  177 
geologic,  179 

for  glass  pots,  179 

Indiana,  312 

Iowa,  321 

Kentucky,  329 

Maryland,  335,  336,  337 

mentioned,  214 


476 


INDEX 


Fire-clay,  Mexico  County,  Mo.,  356 

Missouri,  356,  359 

New  Jersey,  174,  369,  371 

New  Mexico,  373 

New  York,  378 

North  Carolina,  385 

Ohio,  392,  394,  395,  397 

Pennsylvania,  401,  402,  405,  406,  407, 
411 

pholerite,  51 

properties  of,  170,  177 

St.  Louis,  properties  of,  356 

silica-alumina  ratio,  173 

silica  in,  effects  of,  170 

South  Dakota,  419 

Tennessee,  421,  422 

tensile  strength,  122 

Texas,  427,  428,  431 

titanium  in,  effect  of,  176 

United  States,  distribution,  177 

uses  of,  179 

Utah,  434 

vanadates  in,  57 

Virginia,  437 

Washington,  441 

West  Virginia,  445,  446 

See  also  Flint-day 
Fireproofing,  defined,  247 
Fireproofing  clay,  analyses  of,  193 

Indiana,  312 

Massachusetts,  342 

mentioned,  313,  437 

New  Jersey,  193,  364 

New  York,  376 

Ohio,  392 

physical  tests,  194 

properties  of,  192 
Fire- shrink  age,  cause  of,  129 

range  of,  129 

relation  to  texture,  131 

temperature  of,  129 
Flashing  bricks,  189 
Flint,  52,  261,  271,  275 
Flint- clay,  Alabama,  283 

defined,  177 

Kentucky,  392 

Maryland,  385 

mentioned,  40 

Missouri,  354,  355 

Ohio,  396,  397 

origin,  354 

Pennsylvania,  406 

tensile  strength,  122 

West  Virginia,  441,  445,  446 
Flood-plain  clays,  20 
Floor-driers,  236,  252 
Floor- tile,  classification  of,  258 

manufacture  of,  258 

mentioned,  179,  258 

properties  of,  258 

raw  materials,  261 
Florida,  ball-clay,  297 


Florida  clays  described,  297 

fullers'  earth,  461    . 

references  on,  297 
Flower-pot     clay,     California,     289.     See 

Earthenware 

Flue-lining  clay,  Ind.,  313 
Fluorine  as  kaolinizing  agent,  5 
Fluxes  defined,  59 
Folding  in  clay-deposits,  28 
Fond  du  Lac,  Wis.,  455 
Fores tdale,  Vt.,  333 
Forschammer,  cited,  2 
Fort  Smith,  Ark.,  285 
Fort  Worth,  Tex.,  427 
Fox  Hills  group,  S.  Dak.,  389 
Fredericksburg,  Va.,  437 
Frostburg,  Md.,  335 
Fullers'  earth,  Arkansas,  462 

California,  462 

defined,  460 

distribution,  461 

Georgia -Florida  district,  461 

mining  and  uses,  466    . 

New  York,  462 

petrographic  characters,  461 

production,  466 

properties,  460 

South  Dakota,  462 

Southern  States,  462 
Fulton,  Mo.,  356 
Fusibility,  Bischof's  formula,  145 

classification  based  on,  154 

complete  vitrification,  138 

Cramer's  experiments,  141 

expression  of,  145 

factors  influencing,  137 

incipient  vitrification,  138 

Lud wig's  experiments,  142 

measurement  of,  147 

oxidation,  relation  to,  145 

rate  of  softening,  139 

relation  to  chemical  composition.  139 
homogeneity,  144 

Richter's  experiments,  140 

Seger  cones,  148 

Seger's  formula,  146 

texture,  relation  to,  144 

viscosity,  138 

Wheeler's  formula,  146 

See  Pyrometers 
Fusibility-factor,  147 
Fusion  formation,  S.  Dak.,  419 


G 


Gabbro,  1,  400 

Gadsden  County,  Fla.,  461 

Galena-Trenton  formation,  Iowa,  316 

Galesburg,  111.,  304 

Gallia,  Ohio,  398 

Gallipolis,  Ohio,  398 


INDEX 


477 


Garnet,  as  source  of  kaolinite,  47 

mentioned,  68,  70,  71,  76,  83,  385 

occurrence  in  clay,  57 
Garrett  County,  Md.,  335 
Gas-retorts,  179,  196 
Gay  Head,  Mass.,  341 
Geary,  Okla.,  400 
Geijsbeek,  S.,  cited,  423 
Georgia,  clay,  minerals  in,  41 

clays  described,  298 

coastal  plain  clays,  301 

fullers'  earth  in,  461 

halloysite  in,  49 

mentioned,  179,  197 

Pre- Cambrian  clays,  298 

references  on,  303 
Germany,  180 
Gibbsite,  167 
Glacial  clay,  Missouri,  360 

Rhode  Island,  415 

South  Dakota,  420 

Washington,  441 

Wisconsin,  455 

Wyoming,  457. 

See  also  Pleistocene 
Glass-pot  clay,  179 
Glauconite,  analysis  of,  57 

as  coloring  agent,  161 

clays,  57,  68,  70,  71,  83,  427,  431 
Glazes,  Bristol,  271 

porcelain,  275 

pottery,  271,  272 

salt,  271 

terra-cotta,  257 
Glen  Allen,  Mo.,  167,  354 
Gneiss,  278,  334,  340,  434,  452 
Golden,  Colo.,  28,  290 
Goldsboro,  N.  C.,  385 
Graham,  Tex.,  426 
Grand  Gulf  formation,  Ala.,  283 
Grand  Junction,  Tenn.,  422 
Grand  Rapids,  Mich.,  345 
Grand  Rapids,  Wis.,  452 
Granite,  change  to  clay,  7 

disintegration  of,  2 

mentioned,  278,  400 
Grant  County,  W.  Va.,  442 
Great  Valley,  clays  in,  401,  434 
Green  Bay,  Wis.,  455 
Green  brier  County,  W.  Va.,  442 
Greenford,  Ohio,  395 
Green  Lake  County,  Wis.,  455 
Greensand.      See  Glauconite 
Greensand,  Va.,  437' 
Greensboro,  N.  C.,  385 
Greenup  County,  Ky.,  329 
Greenville,  Tex.,  428 
Griffin,  cited,  89 
Grimsley,  cited,  26,  442,  445 
Grinding,  effect  on  plasticity,  104 
Grog,  132 
Gross  -Almerode,  180 


Grout,  cited,  26,  102,  103,  104 

Grover,  N.  C.,  385 

Guillemin,  cited,  50 

Gumbo-clay,  chemical  composition,  196 

Iowa,  322 

Kansas,  327 

Missouri,  122 

physical  properties,  196 

tensile  strength,  122 
Gypsum,  decomposition  temperature,  56 

effect  on  clay,  78 

mentioned,  56,  76,  79,  98, 345,  389,  427 

occurrence  in  clay,  56 


H 


Hackensack,  N.  J.,  19,  371 
Halcyon,  Wis.,  452 
Halle,  Germany,  kaolin  at,  6 
Halloysite,  analyses  of,  49 

dehydration  temperature,  52 

Georgia,  49 

Missouri,  41,  49 

properties  of,  48 

referred  to,  8,  40,  41,  167 
Hall  Station,  N.  C.,  385 
Hamilton  shales,  345,  376,  442 
Hammond,  W.  Va.,  445 
Hampshire  County,  W.  Va.,  442 
Hand -wedging,  265 
Hanover,  Ohio,  392 
Hardy  County,  W.  Va.,  442 
Harford  County,  Md.,  336,  337 
Harmonville,  Pa.,  413 
Harper's  Ferry,  Va.,  434 
Hauyne,  as  source  of  kaolinite,  47 
Haverhill,  Mass.,  342 
Ha  worth,  E.,  cited,  98,  327 
Haydenville,  Ohio,  394,  396 
Hecht,  cited,  148 
Hematite,  54,  71 
Henderson,  Tex.,  431 
Henry  County,  Missouri,  359 
Henry  County,  Tennessee,  423 
Henry  County,  Virginia,  434 
Herzfeld,  cited,  98 
Hice,  R.  R.,  cited,  407 
Hico,  Tenn.,  422 
Hightstown,  N.  J.,  370 
Hirsch,  cited,  163 
Hocking  County,  Ohio,  394,  395 
Hofman,  H.  O.,  cited,  155 
Hollow  blocks,  defined,  248 
Hollow  bricks,  defined,  248 
Hollow  Rock,  Tenn.,  422 
Hollow  ware,  advantages  of,  251 

manufacture  of,  247 

sizes,  248 
Hollow-ware  clays,  304,  316,  321,  359,  407. 

See  also  Fire-proofing  day 
Holly  Springs,  Miss.,  352 


478 


INDEX 


Holyoke,  Mass.,  341 

Horaewood  sandstone,  West  Virginia,  442 

Hope  Station,  Pa.,  406 

Hopkins,  T.  C.,  cited,  401,  402 

Hornblende,  kaolinization  of,  4 
occurrence  in  clay,  57 
referred  to,  41,  68,  70,  71,  83 

Hornellsville,  N.  Y.,  376 

Hot  Springs,  S.  Dak,  419 

Hottinger,  A.,  cited,  81 

Houston,  Tex.,  431 

Howard  County,  Md.,  337 

Howell  County,  Md.,  354 

Hudson  River  shales,  39,  342,  364,  376, 
402,  452 

Hudson  Valley,  19,  378,  381 

Huntington  County,  Pa.,  402 

Huron,  Ind.,  309 

Huron  County,  Mich.,  345 

Huron  shale,  Ohio,  392 

Hydrated  aluminum  silicate,  4,  5 

Hydrolysis,  2 

Hydromica  slates,  as  source  of  kaolin,  401 

Hydrous  silica,  effect  on  clay,  70 


Illinois,  clays  described,  303 

Coal-measure  shales,  304 

drift-clays,  304 

mentioned,  179,  191,  192 

Ordovician  clays,  304 

references  on,  307 

Tertiary  clays,  304 
Ilmenite,  occurrence  in  clay,  56 
Impure  shales,  Missouri,  properties  of,  359 
Independence,  Ohio,  392 
Independence  limestone,  327 
Indian  Territory,  clays  described,  315 
Indiana,  Carboniferous  shales,  309 

clays  described,  307 

coal-measures,  clays  and  shales,  311 

Devonian  shales,  307 

indianaite,  309 

Lower  Carboniferous  shales,  307 

mentioned,  165,  179,  183,  192,  212 

Ordovician  shales,  307 

Pleistocene  clays,  313 

references  on,  313 

Silurian  shales,  307 
Indianaite,  analyses  of,  50 

Indiana,  309 

origin  of,  310 

properties  of,  50 

referred  to,  8 
In  key,  v.,  B.,  cited,  6 
Interlocking  tile,  254 
lola  limestone,  Kan.,  327 
lone,  Cal.,  289 
lone  formation,  289 
Ionia,  Mich.,  346 


Iowa,  Cambrian  shales,  316 

Carboniferous  shales,  318 

clays  described,  316 

coal- measure  clays  and  shales,  321 

Cretaceous  clays,  321 

Devonian  shales,  318 

mentioned,  123,  127,  137,  179 

Ordovician  clays,  316 

Pleistocene  clays,  322 

references  on,  322 

Silurian  shales,  316 
Iron  compounds,  coloring  action,  72 

effect  of  reduction  on,  75 

effect  on  clay,  72 

oxidation  of,  74 
Iron  ores  in  clay,  54 
Iron  oxide,  coloring  action  of,  159,  161,  162 

effect  on  adsorption,  76 

effect  on  clay,  71 

fluxing  action  of,  75 

in  residual  clay,  12 

mentioned,  137,  198  ^ 

relation  to  flashing,  189 

sources  of,  71 
Ironstone  china,  262 


Jackson  Bluff,  Fla.,  297 
Jackson  County,  Ky.,  329 
Jackson  County,  Wis.,  452 
Jackson,  Term.,  pottery  at,  422 
Jacksonville,  Fla.,  297 
James  River,  Va.,  437 
Jauchau  Fu,  kaolin  from,  8 
Jefferson  County,  Ohio,  396 
Jefferson  County,  W.  Va.,  442 
Jennings  shale,  Maryland,  335 
Jewettville,  N.  Y.,  376 
Jiggering,  266 
Johnson,  cited,  48,  51,  97 
Johnson  County,  Wyo.,  458 
Johnstown,  Pa.,  406 
Jollying,  266 
Josingsf j  ord,  kaolin  at,  3 
Juniata  County,  Pa.,  402 
Jurassic,  fullers'  earth  in,  462 
Jura-Trias,  Maryland,  336 


Kansas,  Carboniferous  shales,  326 

clays  described,  326 

Cretaceous,  327 

Pleistocene  clays,  327 

references  on,  327 

Triassic  clays,  327 
Kansas  City,  Mo.,  189 
Kasai,  cited,  100 


INDEX 


479 


Kaolin,  adsorptive  power,  163,  164 

Alabama,  278 

analyses  of,  4,  168 

Arkansas,  285 

china,  11 

chemical  composition,  167 

Colorado,  6 

Cornwall,  England,  5 

defined,  8 

dehydration  temperature,  52 

Delaware,  11,  296 

depth  of,  6 

derivation  of  name,  8 

distribution  of,  167 

European,  sources  of,  165 

garnet  in,  57 

Halle,  Germany,  6 

impurities  in,  167 

Indiana,  309 

Johnson  and  Blake's  definition,  48 

Maryland,  334 

Massachusetts,  340 

mentioned,  11,  83,  84,  100,  198,  214, 
251,271,  298,460 

North  Carolina,  6,  167,  385 

Oklahoma  Territory,  400 

origin  of,  165 

Pennsylvania,  6,  401 

physical  tests  of,  167 

refractoriness  of,  47 

St.  Anstell,  England,  analysis  of,  6 

St.  Yrieux,  France,  analysis  of,  11 

South  Dakota,  419 

Tennessee,  421 

tensile  strength,  122 

Texas,  40,  50,  426 

tourmaline  in,  57 

uses  of ,  168 

Utah,  434 

Vermont,  333 

Virginia,  167,  434 

Zettlitz,  Bohemia,  6 
Kaolin-beds,  so-called,  New  Jersey,  369 
Kaolinite,  defined,  8 

described,  42 

Johnson  and  Blake's  definition,  48 

mentioned,  3,  40,  41,  50,  51,  69,    98, 
136,  167, 170 

minerals  yielding,  47 

Missouri,  355 
Kaolinization  by  pneumatolysis,  5 

defined,  3 

shrinkage  accompanying,  47 
Kaolin  mining,  209,  210,  211 
Kauling,  8 

Kent's  Island,  Mass.,  340 
Kentucky,  Carboniferous  clays,  328 

clays  described,  328 

Devonian  clays,  328 

mentioned,  169,  178,  179 

Ordovician  clays,  328 

Pleistocene  clays,  329 


Kentucky,  references  on,  330 

Tertiary,  329 

Kern  County,  Cal.,  fullers'  earth  in,  462 
Key  port,  N.  J.,  370 
Kilns,  continuous,  239 

described,  236 

down- draft,  239 

mentioned,  251,  252,  258 

pottery,  272 

Kinderhook  shales,  Iowa,  318 
Kingman,  Kan.,  327 
Kingsland,  N.  J.,  364 
King-te-chin,  porcelain  of,  8 
Kingwood,  W.  Va.,  446 
Kinkora,  N.  J.,  370 
Kittanning,  Pa.,  406 
Kittanning  clays,  W.  Va.,  445 
Knight,  W.  C.,  cited,  457 
Knobstone  shales,  Indiana,  307 
Knop,  cited,  50 

Knox  dolomite,  Tennessee,  421 
Kohler,  cited,  164 
Koninck,  cited,  50 
Kovar,  cited,  85 
Kreischerville,  N.  Y.,  378 
Kummer,  Wash.,  441 


Labradorite,  kaolinization  of,  4 
Lacka wanna  County,  Pa.,  402 
La  Crosse,  Wis.,  456 
Lacustrine  clays,  Wisconsin,  455 
Ladd,  G.  E.,  cited,  24,  41,  103,  105 
Lafayette  sands,  Tenn.,  422 
Lagatu,  cited,  41 
La  Junta,  Colo.,  290 
Lake -clays,  20 
Lake  County,  Ind.,  313 
Lampasas  County,  Tex.,  426 
Lancaster,  N.  Y.,  378 
Langenbeck,  cited,  105 
Laporte  County,  Ind.,  313 
Laramie  County,  Wyo.,  458 
Laramie  clays,  North  Dakota,  389 

South  Dakota,  419 
Laredo,  Tex.,  428,  431 
Las  Vegas,  N.  Mex.,  373 
Lawrence  County,  Ind.,  50,  309 
Lawrence  County,  Ky.,  329 
Lawrence  County,  Mo.,  354 
Lawrence  County,  Ohio,  396 
Lawrence  County,  Pa.,  405 
Lawrence  shales,  327 
Lead,  S.  Dak.,  420 
Lead  salts,  adsorption  by  clay,  163 
Leaky,  Tex.,  50,  426 
Le  Chatelier,  H.,  cited,  48,  51,  52 
Leda  clays,  41 
Lehi,  Utah,  434 
Leon  County,  Fla.,  461 


480 


INDEX 


Lepidolite,  occurrence  in  clay,  54 

solubility  of,  2 
Lesquereaux,  cited,  310 
Leucite,  as  source  of  kaolinite,  47 

solubility  of,  2 
Leucoxene,  56 
Lignite,  389 

with  fire-clay,  S.  Dak.,  419 
Lignitic  clays,  Tex.,  428 
Lime,  adsorption  by  clay,  163 

as  coloring  agent,  159,  162 

determination  of,  65 

effect  on  clays,  76 

effect  on  iron  coloration,  73 

source  of,  in  clay,  76 
Lime  carbonate,  bleaching  effect,  77 

decarbonation  temperature,  76 

effect  on  clay,  76 

relation  to  vitrification,  77 
Lime  silicates,  effect  on  clay,  78 
Limestone,  alteration  to  clay,  7 

as  source  of  kaolin,  165 
Limonite,  mentioned,  41,  71,  193,  203 

occurrence  in  clay,  54 

Vermont,  333 
Lincoln,  Cal.,  289 
Lincolnton,  N.  C.,  385 
Linder,  cited,  97 
Lindgren,  cited,  6,  289 
Linn  County,  Iowa,  318 
Little  Falls  Station,  Wash.,  441 
Little  Rock,  Ark.,  285 
Littoral  clays,  25 
Lloyd,  Tex.,  427 
Loess,  analyses  of,  187 

distribution,  186 

Iowa,  322 

mentioned,  186,  304 

Missouri,  360 

Nebraska,  363 

tensile  strength,  122 

Wisconsin,  456 

Wyoming,  457 
Logan  shale,  Ohio,  392 
Log-washer,  162 
Long  Island,  N.  Y.,  378 
Lorraine  shale,  Ohio,  391 
Los  Angeles,  Cal.,  289 
Louisiana,  clays  described,  331 

references  on,  332 
Lower  Barren  Measures.     See  Conemaugh 

series 
Lower  Carboniferous,  Missouri,  355 

Ohio,  392,  394 

West  Virginia,  442 
Lower  Cretaceous,  New  Jersey,  366 

Texas,  426 
Lower  Freeport  clay,  Ohio,  394,  397 

Pennsylvania,  408 
Lower  Kittanning  clay,  Ohio,  394,  395 

Pennsylvania,  406,  407 

West  Virginia,  445 


Lower  Mercer  clay,  Ohio,  393,  394 

iron  ore,  Ohio,  393 

limestone,  Ohio,  393 

Lower    Productive    Measures.     See    Alle- 
gheny series 
Lucas,  cited,  100 
Ludwig,  cited,  142 
Lunette  pyrometer,  153 
Luzerne  County,  Pa.,  402 


Ai 


McConnellsville,  N.  Y.,  462 

McKean  County,  Pa.,  402 

Mt.  Savage  fire-clay,  Pennsylvania,  405 

West  Virginia,  442 
Mt.  Savage,  Maryland,  335 
Mackenzie,  Tenn.,  422 
Mackler,  cited,  80,  91 
Macon,  Ga.,  301 
Magnesia,  determination  of,  65 

effect  on  clay,  80,  81 

Mackler's  experiments  with,  80 
Magnesite,  occurrence  in  clay,  57 
Magnesium,  adsorption  of,  by  clay,  163 
Magnetite,  41,  55,  71 
Mahoning  sandstone,  West  Virginia,  446 
Maine,  clays  described,  333 
Majolica,  defined,  262 
Malakoff,  Tex.,  431 
Malthacite,  460,  461 
Manganese,  in  clay,  58,  198 

Vermont,  333 
Mangum,  Okla.,  400 
Manitowoc  County,  Wis.,  455 
Mansfield  sandstone,  309,  311 
Manufacture  of,  bricks,  218 

conduits,  251 

drain-tile,  247 

fire-brick,  252 

floor-tile,  258 

hollow  ware,  247 

pottery,  262 

roofing- tile,  254 

sewer- pipe,  240 

terra-cotta,  254 
Maple  Shade,  N.  J.,  370 
Maquoketa  shale,  316 
Marathon  County,  Wis.,  452 
Marble,  adsorptive  power  of  ground,  163 
Marine  beds,  Texas,  431 
Marine  clays,  19 
Marion  County,  Tenn.,  421 
Marly  clays,  Indiana,  313 

Texas,  427 

Marquette,  Mich.,  346 
Marshall  clays,  Michigan,  345 
Marshall  County,  Miss.,  352 
Martha's  Vineyard,  Mass.,  341 
Martin  County,  Ind.,  309 
Martinsburg  shale,  West  Virginia,  442 


INDEX 


481 


Martins ville,  Ind.,  309 
Maryland,  Algonkian  clays,  334 

Arundel  clays,  337 

Carboniferous  shales,  335 

clays  described,  334 

Cretaceous  clays,  336 

Devonian  shale,  335 

glauconite  in,  57 

Jura- Trias  clays,  336 

mentioned,  58,  101,  178,  179,  191,  198, 
212 

Patapsco  clays,  337 

Pleistocene  clays,  337 

Raritan  clays,  337 

references  on,  339 

Silurian  shales,  334 

Tertiary  clays,  337 
Massachusetts,  clays  described,  340 

Cretaceous  and  Tertiary  clays,  341 

kaolins,  340 

Pleistocene  clays,  341 

references  on,  342 
Mason  City,  Iowa,  318 
Masontown,  W.  Va.,  446 
Massillon  sandstone,  Ohio,  393 
Matawan,  N.  J.,  370 
Matawan  formation,  336 
Mauch  Chunk  shale,  335,  402,  442 
Maxville  limestone,  clay  in,  392 
Maynard  ville,  Tenn.,  423 
May's  Landing,  N.  J.,  371 
Mecca,  Ind.,  313 
Mechanical  analysis,  Beaker  method,  110 

centrifugal  method,  115 

described,  108 

Hilgard  method,  114 

Iowa  clays,  127 

New  Jersey  clays,  125 

residual  clays,  14 

Schoene's  method,  113 
Medford,  Mass.,  341 
Medina  shale,  376,  442 
Meigs  County,  Ohio,  398 
Mellor,  J.  W.,  cited,  103 
Menomonie,  Wis.,  456 
Mercer  clay,  Pa.,  402 
Mercer  County,  Pa.,  405 
Merill,  G.  P.,  cited,  41,  49,  128,  461 
Merillan,  Wis.,  452 
Mertztown,  Pa.,  401 
Mesozoic,  52,  285 
Meta-sedimentary  clays,  25 
Mexico,  Mo.,  356 
Mica,  occurrence  in  clay,  53 

compared  with  kaolin,  47 

mentioned,  2,  68,  70,  210,  385 
Michigan,  Carboniferous  shales,  345 

clays  described,  342 

Devonian  shales,  345 

mentioned,  56,  78,  179 

Pleistocene,  346 

references  on,  347 


Michigan,  Silurian  shales,  342 
Michigan  shale  formation,  345 
Microcline,  adsorptive  power  of,  164 

as  source  of  kaolinite,  47 
Middle  Kittanning  clay,  Ohio,  394,  397 

Pennsylvania,  407 

West  Virginia,  445 
Middletown,  Conn.,  295 
Millard  County,  Utah,  434 
Milldale,  Conn.,  295 
Millersburg,  Ohio,  394 
Millsap,  Tex.,  426 
Millville,  N.  J.,  371 
Mineral  County,  W.  Va.,  442 
Minerals  in  clay,  40 
Mingo  clay,  Ohio,  394 
Mingo  County,  W.  Va.,  446 
Mining  clay,  205 
Minneapolis,  Minn.,  351 
Minnekata,  S.  Dak.,  fullers'  earth  at,  463 
Minnesota,  clays  described,  348 

Cretaceous  clays,  348 

Ordovician  clays,  348 

Pleistocene  clays,  351 

Pre- Cambrian  clays,  348 

references  on,  351 

residual  clays,  348 
Minorsville,  Neb.,  363 
Minot,  N.  Dak.,  390 
Miocene  clays,  83,  437 
Mississippi  clays,  described,  352 

references  on,  352 
Mississippian,  354 
Missouri,  ball-clays,  355 

clays  described,  352 

Coal- measure  clays,  356 

fire-clays,  356 

flint-clays,  40,  354 

halloysite,  41,  49 

kaolins,  354 

mentioned,   122,   137,   167,  169,  178, 
179,  180,  181,  183,  212 

Palaeozoic  limestone  clays,  354 

pholerite,  51 

Pleistocene  clays,  360 

references  on,  360 

stone  ware -clays,  355,  359 

Tertiary  clays',  360 
Miston,  Miss.,  352 
Mogadore,  Ohio,  potteries,  394 
Molding  pottery,  266 
Monkton,  Vt.,  333 
Monmouth  formation,  336 
Monongahela  series,  Ohio,  398 

West  Virginia,  446 
Monroe  County,  Ohio,  398 
Monroe  County,  W.  Va.,  442 
Montague,  Tex.,  426 
Montezuma,  Ind.,  313 
Montgomery  County,  Iowa,  321 
Montmorillonite,  51,  52 
Moraine  clays,  346,  378 


482 


INDEX 


Morgan  County,  Mo.,  354 
Morgan  town,  N.  C.,  385 
Morgan  town,  W.  Va.,  446 
Morristown,  Tenn.,  423 
Mound  City,  111.,  304 
Mounds ville,  W.  Va.,  446 
Mount  Holly,  N.  C.,  385 
Mount  Savage  clay,  Ohio,  393,  394 
Moxahala,  Ohio,  397 
Muscovite,  fluxing  action  of,  83 

mentioned,  2,  41,  83,  136,  167 

occurrence  in  clay,  54 

solubility  of,  2 
Muskingum  County,  Ohio,  394,  395,  396 


Nacogdoches,  Tex.,  431 
Nacrite,  defined,  51 
Nageli,  cited,  99 
Nan  tucket,  Mass.,  341 
Narragansett  Bay,  R.  I.,  415 
Natrona  County,  Wyo.,  458 
Nebraska,  Carboniferous  clays,  362 

clays  described,  362 

Cretaceous  clays,  363 

loess,  363 

references  on,  364 
Nebraska  City,  Neb.,  362 
Neocene,  289 
Nephelinite,  as  source  of  kaolinite,  47 

solubility  of,  2 
New  Albany,  Ind.,  309 
Newark,  Ohio,  392 
New  Boston,  Tex.,  428 
New  Brighton,  Pa.,  407 
New  Brighton  clay,  407 
New  Cumberland,  W.  Va.,  445,  446 
Newell,  155 

New  Hampshire,  clays  described,  333 
New  Jersey,  Cambrian  clays,  364 

clays  described,  364 

Cretaceous  clays,  366 

glauconite  in,  57 

mentioned,  39,  55,  84,  123,  125,  137, 
169,  174,  179,  181,  183,  188,  192, 
196,  205 

pholerite  in  fire-clays  of,  51 

Pleistocene  clays,  371 

Ordovician  shales,  364 

references  on,  373 

Tertiary  clays,  370 

Triassic  shales,  364 
New  Lexington,  Ohio,  395 
New  Mexico,  clays  of,  373 
Newton  County,  Ind.,  313 
Newtonite,  properties  of,  51 
New  Ulm,  Minn.,  351 
New  York,  clays  described,  375 

Cretaceous  clays,  378 

fullers'  earth  in,  462 


New  York,  clays  mentioned,  39,  56,  181, 
191,  192 

Paleozoic  shales,  375 

Pleistocene  clay,  378 

references  on,  382 

residual  clays,  375 

Tertiary  clays,  378 
Niagara  shale,  N.  Y.,  376 
Niobrara  formation,  N.  Dak.,  389 
Norfolk,  Va.,  437 
North  Carolina,  clays  described,  382 

fullers'  earth  in,  462 

kaolins,  385 

mentioned,  6,  57,  69,  167 

references  on,  388 

residual  clays,  385 

sedimentary  clays,  385 
North  Dakota,  clays  described,  389 

Cretaceous  clays,  389 

Laramie  clays,  389 

Pleistocene  clays,  390 

references  on,  390 

Tertiary  clays,  389 
Northeast,  Md.,  334 
Northport,  N.  Y.,  181 


Oakfield,  Wis.,  455 

Oak  Hill,  Ohio,  397 

Oak  Level,  Va.,  167 

Oaxanna,  Ala.,  283 

Ocher,  198 

Odernheimer,  cited,  35 

Ohio,  Allegheny  series  clays,  394 

Brookville  clay,  394 

clays  described,  390 

Coal -measure  clays,  392 

Conemaugh  series  clays,  398 

Devonian  shales,  392 

Dunkard  series,  398 

ferriferous  limestone  clay,  395 

Lower  Carboniferous  clays,  392 

Lower  Freeport  clay,  397 

Lower  Kittamiing  clay,  395 

Lower  Mercer  clay,  394 

mentioned,  84,  178,  179,  191,  192 

Middle  Kittanning  clay,  397 

Monongahela  series,  398 

Mount  Savage  clay,  394 

Ordovician,  390 

Pleistocene,  398 

Pottsville  series,  393 

Putnam  Hill  clay,  394 

Quakertown  shale,  393 

references  on,  399 

Sharon  shales,  393 

Silurian,  390 

Upper  Freeport  clay,  397 

Upper  Mercer  clays,  394 
Ohio  River  region,  Pa.,  407,  408,  413 


INDEX 


483 


Ohio  shale,  Ohio.  392 

Oklahoma  clays  described,  400 

Olciie.vsky,  cited,  97,  98,  101 

Oletangy  saale,  Ohio,  392 

Oligocene,  fullers'  earth  in,  462 

Oligoclase,  solubility  of,  2 

Olive  Hill,  Ky.,  329 

Ontario,  Medina  brick  shale  in,  376 

Oolite,  Okla.,  316 

Open  yards .  described,  232 

Ordovician  clays,  Kentucky,  328 

Iowa,  316 

limestone  residuals,  452 

Minnesota,  348 

Missouri,  355 

Ohio,  390 

Wisconsin,  452 
Oread  limestone,  327 
Ore  Hill,  Pa.,  401 
Orthoclase,  41,  83 

adsorptive  powers,  164 

as  source  of  kaolinite,  47 

effect  of  fluorine  on,  5 

kaolinization  of,  3 

reaction  with  water,  3 

solubility  of,  2 

Orton,  E.,  cited,  73,  89,  97,  180,  392 
Orton,  Jr.,  K,  cited,  23,  26,  123,  124,  392 
Osgood  shale,  Ohio,  391 
Ouachita  County,  Ark.,  285 
Owen  County,  Ind.,  309 
Owosso,  Mich.,  345 


Paint-clay,  Missouri,  354 

properties  of,  198 
Palaeozoic  clays,  Georgia,  298 

New  York,  375 
Pallet-driers,  described,  232 

referred  to,  247,  251 
Paper  clays,  Missouri,  354 

Pennsylvania,  401 

properties,  197 

sources,  197 

South  Carolina,  416 

Vermont,  333 
Paris,  Tex.,  427 
Parkers  burg,  W.  Va.,  449 
Parkville,  Pa.,  406 
Parrot  River,  England,  199 
Patapsco,  Md.,  337 
Patrick  County,  Va.,  434 
Patuxer.t,  Md.,  336 
Paving-brick  clays,  composition  of,  191,  192 

Indiana,  312, 313 

Iowa,  192, 321 

Kansas,  326 

Kentucky,  329 

Maryland,  335 

Michigan,  345 


Paving -brick  clays,  Missouri,  359 

Nebraska,  363 

New  York,  376,  378 

Ohio,  392,  395,  397,  398 

Pennsylvania,  402,  407,  413 

properties  of,  191 

Texas,  426,  427,  431 

Virginia,  437 

West  Virginia,  445,  446 

Wisconsin,  452 
Peaceburgh,  Ala.,  283 
Pegmatite,  as  source  of  kaolin,  165,  402 

referred  to,  11,  340,  385 
Pegram,  Ala.,  283 
Pelagic  clays,  25 
Pembina,  N.  Dak.,  389 
Pendleton  County,  W.  Va.,  442 
Pennsylvania,  Allegheny  series  clays,  405 

Alton  fire-clay,  402 

Brookville  clay,  405 

clays  described,  401 

Darlington  clay,  407 

Devonian  shales,  402 

Carboniferous  clays,  402 

Clarion  clay,  406 

Conemaugh  series  clays,  411 

ferriferous  coal  under- clay,  406 

kaolin,  6 

Lower  Barren  Measures,  411 

Lower  Freeport  clay,  408 

Lower  Kittanning  clay,  406 

Mount  Savage  fire-clay,  405 

Mercer  fire-clay,  402 

Middle  Kittanning  clay,  407     • 

Monongahela  series  clays,  413 

Pleistocene  clays,  413 

Pottsville  clays,  402 

references  on,  414 

referred  to,  39,  84,  178,  179,  180,  183, 
191,  192,  198,  212 

residual  clays,  401 

Sharon  upper  coal  fire-clay,  405 

Silurian  shales,  402 

Upper  Coal-measures,  413 

Upper  Freeport  clay,  41 1 

Upper  Kittanning  clay,  407 
Pennsylvania  clays,  Indian  Territory,  315 

Oklahoma,  400 
Penn  Yan,  N.  Y.,  376 
Penrose,  cited,  6 
Permeability  of  clay,  163 
Permian  clays,  Indian  Territory,  315 

Nebraska,  362 

Oklahoma,  400 

West  Virginia,  449 
Perry  County,  Ohio,  395 
Perry  County,  Pa.,  402 
Perth  Amboy,  N.  J.,  209 
Peru,  Neb.,  363 
Petersburg,  Va.,  437 
Pe-tun-tse,  11 
Phenolphthalein,  2 


484 


INDEX 


Philadelphia,  Pa.,  413 
Phlogopite,  solubility  of,  2 
Pholerite,  in  fire-clays,  51 

in  Missouri  clays,  51,  355 

properties  of,  50 

referred  to,  40,  167 
Physical  properties  of  clay,  94 
Physical  tests  of  clays,  Alabama,  284 

Georgia,  303 

Maryland,  339 

Michigan,  347 

Missouri,  361 

New  Jersey,  374 

New  York,  381 

North  Carolina,  387 

Texas,  431 

Virginia,  438 

West  Virginia,  450 
Piedmont,  W.  Va.,  445 
Piedmont  region,  residual  clays  of,  12 
Pierre  shales,  North  Dakota,  389 

South  Dakota,  419 
Pike  County,  Ark.,  285 
Pine  Grove,  Pa.,  402 
Pinkerton  Point,  Pa.,  406 
Pinson,  Tenn.,  422 
Pipe-clay,  defined,  196 
Pipe-press,  described,  240 
Pittsburg,  Kan.,  326 
Pittsburg,  Pa.,  shales  at,  411 
Pitteburg  coal,  clay  parting  in,  413 

referred  to,  398,  411,  446 
Plagioclase,  as  source  of  kaolmite,  3,  47 

mentioned,  41 
Plasticity,  ball  theory  of,  99 

cause  of,  96 

colloid  theory  of,  99 

defined,  94 

effect  of  bacteria  on,  104 

effect  of  weathering  on,  104 

molecular  attraction  theory  of,  103 

plate  theory  of,  97 

relation  to  tensile  strength,  120 

texture  theory  of,  96 

water  necessary  for  developing,  95 

water-of-h  yd  ration  theory,  96 
Platteville,  Wis.,  455,  456 
Pleistocene  clays,  Alabama,  283 

Colorado,  290 

Connecticut,  295 

Indiana,  313 

Iowa,  322 

Kansas,  327 

Maryland,  337 

mentioned,  52,  58,  185,  192,  285,  295 

Michigan,  346 

Minnesota,  351 

Mississippi,  352 

Missouri,  360 

New  Jersey,  371 

New  York,  378 

North  Dakota,  390 


Pleistocene  clays,  Ohio.  398 

Pennsylvania,  413 

South  Dakota,  419 

Texas,  431 

West  Virginia,  437,  449 

Wisconsin,  455 
Pleistocene  fullers'  earth,  465 
Plymouth,  Vt,  333 
Plymouth  County,  Iowa,  321 
Pocahontas  County,  \\ .  Va.,  442 
Polishing  clay,  199 
Pomona,  N.  C.,  385 
Porcelain,  bone,  defined,  272 

electrical,  275 

manufacture  of,  271 

spar,  defined,  272 
Porcelain-clay.     See  Kaolin 
Porosity,  discussion  of,  134 

formula  for  calculating,  136 

of  Iowa  clays,  135 

practical  bearing  of,  135 
Portage  County,  Ohio,  394 
Portage  County,  Wis.,  452 
Portage  shale,  New  York,  376 
Porter  County,  Ind.,  313 
Port  Huron,  Mich.,  346 
Portland-cement  clay,  analyses,  198 

properties  of,  198 
Port  Murray,  N.  J.,  364 
Portsmouth,  Chio,  392 
Potash,  in  clay,  82 
Pot-clay,  196,  214 
Potomac  clays,  296,  336,  352,  415 
Potsdam,  residual  clay  from,  12 
Potsdam  sandstone,  A\  isconsin,  452 
Potsdam  shales,  Wisconsin,  452 
Pottery,  bath-tubs,  276 

china,  defined,  262 

classification,  262 

common  earthenware,  defined,  262 

C.  C.  ware,  defined,  262 

fayence,  defined,  262 

ironstone  china,  262 

majolica,  defined,  262 

Rockingham  ware,  defined,  262 

sanitary  ware,  276 

semi-porcelain,  262 

semi-vitreous  ware,  262 

stoneware,  defined,  262 

wash-tubs,  276 

white  granite  ware,  defined,  262 

white  ware,  262 

yellow  ware,  defined,  262 
Pottery  clays,  California,  289 

Illinois,  304 

Kentucky,  328 

Maryland,  337 

Massachusetts,  341 

Nebraska,  363 

Ohio,  394,  395,  396 

Pennsylvania,  406,  407 

South  Dakota,  419 


INDEX 


485 


Pottery  clays,  Tennessee,  421,  422 

tensile  strength  of,  122 

Texas,  426 

See  also   Stoneware,  Ball-clays,  and 

Kaolin 

Pottery  manufacture,  263 
Potts ville,  Md.,  335 
Potts ville,  Pa.,  402 
Pottsville  series,  Pennsylvania,  393 

West  Virginia,  442 
Pre-Cambrian  clays,  residual,  12 

Georgia,  298 

Minnesota,  348 

Tennessee,  421 

Wisconsin,  452 
Pressed-brick  clays,  Indiana,  312 

Iowa,  321 

Kansas,  326 

Maryland,  337 

Massachusetts,  342 

Minnesota,  348 

New  York,  376 

Ohio,  392,  395 

Pennsylvania,  406 

Texas,  426,  428 

Wisconsin,  456 
Pressing,  269 

Preston  County,  Virginia,  442 
Prince  George  County,  Md.,  336,  337 
Princeton,  Minn.,  351 
Prochlorite,  41 
Prosser,  cited,  327,  392 
Pug- mill,  described,  220 

mentioned,  240,  247,  252, 257,  265,  266 
Pulaski  County,  Ark.,  285 
Pulaski  County,  111.,  304 
Pulaski  County,  Ky.,  329 
Putnam  Hill  clay,  Ohio,  394 
Pycnometer,  137 
Pyrite,  mentioned,36,  71, 193,  311,  389,  427 

occurrence  in  clay,  55 

temperature  of  desulphurization,  74 

weathering  of,  55 
Pyrometer,  Lunette,  154 

Seger  cones,  148 

thermo-electric,  153 

Wedge  wood,  154 
Pyrophyllite,  dehydration  temperature,  52 

mentioned,  51,  98 
Pyroxene,  41 


Q 


Quakertown  clay  and  shale,  Ohio,  393 
Quakertown  coal,  Ohio,  393 
Quartz,  effect  on  clay,  53 

origin,  4 

referred  to,  11,  41,  47,  48,  69,  77,  83, 
136,  170,  210,  257,  385 

weathering  of,  4 
Quartzite,  as  source  of  kaolin,  165,  293 


Quaternary.     See  Pleistocene 

fullers'  earth  in,  462 
Queen's  Run,  Pa.,  406 


R 


Racine,  Wis.,  455 
Raleigh  County,  W.  Va.,  446 
Rancocas  formation,  Md.,  336 
Randolph  County,  W.  Va.,  442 
Ransome,  F.  L.,  cited,  6,  286 
Rapid  City,  S.  Dak.,  419,  420 
Rare  elements  in  clay,  58 
Raritan  formation,  Maryland,  336 

New  Jersey,  366 

Rational    analysis,     compared   with   ulti- 
mate analysis,  62 

described,  61 

method  of  making,  66 
Reading, 'Pa.,  402 
Rectorite,  properties  of,  51 
Red  Oak,  Iowa,  321 

Red  Mountain,  Colo.,  kaolinite  crystals,  42 
Red  Wing,  Minn.,  348 
Reeds  ville,  W.  Va.,  446 
Re-pressing  process,  232 
Residual  clays,  analyses  of,  13 

Appalachian  region,  12 

California,  286 

color  of,  12 

Connecticut,  293 

defined,  7 

depth  of,  12 

distribution  of,  12 

form  of  deposit,  11 

from  granite,  7 

from  limestone,  7 

from  pegmatite  veins,  11 

Georgia,  298 

Indiana,  307 

Maryland,  334,  335 

Massachusetts,  340 

mechanical  analyses,  14 

Minnesota,  348 

Missouri,  354 

New  Jersey,  364 

New  York,  375 

North  Carolina,  385 

origin  of,  7 

Pennsylvania,  401 

Piedmont  region,  12 

rate  of  formation,  12 

South  Carolina,  415 

Tennessee,  421 

United  States,  12 

Vermont,  333 

Virginia,  434 

Washington,  441 

West  Virginia,  442 

Wisconsin,  12,  452 
Retort-clay,  196 


486 


INDEX 


Rhode  Island,  clays  described,  415 

references  on,  415 
Richmond,  Va.,  98,  437 
Richmond  shale,  Ohio,  391 
Richter,  cited,  140,  142,  143 
Richthofen,  v.,  cited,  8 
Ries,  cited,  101, 104, 125, 137,  144,  461,  466 

classification  of,  27 
Riley,  Ind.,  313 
Ring -pits,  220,  252 
Rochester,  N.  Y.,  376 
Rock  Castle  County,  Ky.,  329 
Rockford,  Iowa,  318 
Rockingham  ware,  defined,  262 

manufacture  of,  270 
Rockingham  ware  clay,  Ohio,  397 
Rock  Run,  Ala.,  283 
Rockwell,  G.  A.,  cited,  155 
Rohland,  P.,  cited,  100 
Rolls,  described,  219 
Roman  tile,  254 
Roofing-tile,  described,  254 

manufacture  of,  254 

varieties  of,  254 
Roofing-tile  clays,  Illinois,  304 

Kansas,  326 

Missouri,  359 

New  York,  378 

Ohio,  393 

West  Virginia,  446,  449 
Rosenbusch,  cited,  42 
Rosenhayn,  N.  J.,  371 
Rosier,  cited,  6,  47 
Rusk,  Tex.,  431 
Russell,  I.  C.,  cited,  186 
Rutile,  occurrence  in  clay,  56 


S 


Sac  County,  Iowa,  321 
Safford,  J.  M.,  cited,  421,  422 
Sagger-clay,  defined,  196 

Ohio,  397 
Saggers,  262,  272 
Saginaw,  Mich.,  345,  346 
St.  Austell,  England,  kaolin  at,  6 
St.  Charles,  Mich.,  345 
St.  Joseph  County,  Ind.,  313 
St.  Louis,  Mo.,  84,  356 
St.  Louis  clay,  silica  in,  69 
Salem,  Mass.,  342 
Salina,  Kan.,  327 
Salina,  Pa.,  411 
Salina  shales,  gypsum  in,  56 

New  York,  376 
Salisbury,  R.  D.,  cited,  41 
Saltzburg  sandstone,  W.  Va.,  446 
Saluda  shale,  Ohio,  391 
San  Antonio,  Tex.,  431 
San  Bernardino  County,  Cal.,  fullers'  earth, 
462 


Sand,  effect  on  shrinkage,  129 

Sand-blast,  257 

Sandstone,  residual  clay  from,  12 

Sand-wheels,  213 

Sandy  Ridge,  Pa.,  406 

Sandy  Run,  Pa.,  402 

Saspamco,  Tex.,  431 

Sayreville,  N.  J.,  369 

Scapolite,  as  source  of  kaolinite,  47 

solubility  of,  2 
Schist,  as  source  of  kaolin,  165 

formation  of,  36 

referred  to,  434,  452 
Schlossing,  cited,  100 
Schorl,  210 
Schrotterite,  51 
Sciotoville,  Ohio,  329,  392 
Scranton,  Ohio,  395 
Scumming,  157 
Sebewaing,  Mich.,  345 
Sections,  Bellaire,  Ohio,  397 

Brazil,  Ind.,  311 

Currier,  Tenn.,  423 

Edgar,  Fla.,  297 

Fairburn,  S.  Dak.,  462 

Georgia  fullers'  earth,  462 

Grand  Junction,  Tenn.,  422 

Indiana  Coal-measures,  311 

kaolin -deposit,  13 

Lewis  ton,  Ga.,  301 

New  Cumberland,  W.  Va.,  445 

residual  clay -deposit,  7 

Upper  Ohio  River,  405 

Zanesville,  Ohio,  395 
Sedimentary  clays,  described,  14 

classification  of,  18 

Cretaceous,  17 

distinguished  from  residual,  17 

estuarine  type,  19 

flood -plain  type,  20 

lake  type,  20 

marine  type,  19 

origin,  14 

structural  irregularities,  17 

swamp  type,  20 

Tertiary,  17 

variations  in,  17 
Seger,  H.,  cited,  73,  74,  77,  85,  94, 101,  104, 

148,  174 

Seger  cones,  148 
Selenite,  56 

Semi-dry  press  process,  described,  231 
Semi-porcelain,  defined,  262 
Semi-vitreous  ware,  defined,  262 
Semper,  cited,  6 
Serpentine,  as  source  of  clay,  1 
Settling-tanks,  214 
Sewanee  coal,  fire-clay  with,  421 
Sewell,  Md.,  337 
Sewer-pipe  clays,  described,  183 

distribution,  185 

Indiana,  309,  312,  313 


INDEX 


487 


Sewer  .pipe  clays,  Indian  Territory,  316 

Maryland,  337 

Micuigan,  345 

Missouri,  359 

North  Carolina,  386 

Ohio,  392,  393,  397 

Pennsylvania,  411 

properties  of,  183 

Texas,  431 

Washington,  441 

West  Virginia,  445 
Sewer-pipe  manufacture,  240 
Shaftsbury,  Vt,  333 
Shale,  adsorptive  power,  164 

formation  of,  164 

tensile  strength,  122 
Sharon  clay,  Ohio,  393 

Pennsylvania,  405 
Sharon  coal,  Ohio,  393,  394 
Sharon  sandstone,  Ohio,  393 
Sharon  shale,  Ohio,  393 
Shawano,  Wis.,  455 
Sheboygan,  Wis.,  455 
Shenandoah  limestone  clay,  W.  Va.,  442 
Shepherdstown,  W.  Va.,  442 
Sherman,  Tex.,  427 
Shingle  tile,  254 
Shirley's  Mills,  Ala.,  283 
Shrinkage,  cubic,  Iowa  clays,  135 

measurement  of,  132 

See  also  Air-  and  Fire-shrinkage 
Siderite,  decarbonation  temperature,  74 

forms  of,  55 

occurrence  in  clay,  55 

referred  to,  71 
Sienna,  198 
Sieverxi,  S.  C.,  416 
Silica,  amount  in  clays,  69 

combined,  68 

determination  of,  65 

effect  on  clay,  69 

fluxing  action,  70,  140 

free,  68 

hydrous,  70 

minerals  containing,  68 
Silica  brick,  Pa.,  402 
Sillimanite,  as  source  of  kaolinite,  47 
Silurian  clays,  Indian  Territory,  316 

Iowa,  316 

Kentucky,  328 

Maryland,  335 

Michigan,  342 

New  York,  376 

Ohio,  390 

Pennsylvania,  402 
Slaking  clays,  162 
Slip-clays,  analyses  of,  195 

fluxes  in,  195 

New  York,  195 

properties,  193 

Texas,  431 

uses,  195 


Slip  pump,  214 
Smectite,  460,  461 
Smith,  J.  L.,  cited,  50 
Smith ville,  Tenn.,  421 
Smock,  J.  C.,  cited,  137 
Snyder  County,  Pa.,  402 
Soak-pit,  described,  220 
Socorro,  N.  Mex.,  373 
Soda,  effect  on  clay,  82 

minerals  serving  as  source,  82 
Sodalite,  as  source  of  kaolinite,  47 
Soft- mud  process,  220,  252 
Solubility  of  minerals,  2 
Soluble  salts,  90,  182,  345 

origin  of,  90 

prevention  of,  92 

quantity  in  bricks,  91 
South  Amboy,  N.  J.,  181,  369 
South  Amboy  fire-clay,  369 
South  Carolina,  clays  described,  415 

coastal  plain  clays,  41  ii 

fullers'  earth,  462 

referred  to,  179,  198 

residual  clays,  415 

white  clays,  416 
South  Dakota,  clays  described,  419 

fullers'  earth,  462 

references  on,  420 
South  Hadley,  Mass.,  341 
South  Haven,  Mich.,  346 
South  Mountain,  Pa.,  white  clay,  401 
South  River,  N.  J.,  369 
Specific  gravity,  discussion  of,  136 

determination  of,  137 

Iowa  clays,  137 

minerals  in  clay,  136 

Missouri  clays,  137 

New  Jersey  clays,  137 
Spencer,  J.  W.,  cited,  301 
Spilman,  W.  Va.,  446 
Spodumene,  solubility  of,  2 
Springs,  relation  to  clay-beds,  163,  199 
Stafford  Court  House,  Md.,  437 
Stark  County,  Ohio,  394,  395,  396 
Starke  County,  Ind.,  313 
Staten  Island  clay,  rutile  in,  56 
Steindorfel,  460 
Steubenville,  Ohio,  398 
Stevens  Point,  Wis.,  452 
Stewart  County,  Tenn.,  421 
Stiff-mud  machine,  254 
Stiff-mud  process,  described,  228 

referred  to,  247,  251,  252 
Stockbridge,  Wis.,  455 
Stockton,  Cal.,  289 

Stone  Mountain,  Ga.,  halloysite  at,  49 
Stoneware,  defined,  262 

manufacture,  270 
Stoneware-clay,  chemical  composition,  180 

Connecticut,  295 

Delaware,  296 

Indiana,  312 


488 


INDEX 


Stone  ware -clay,  Iowa,  321 

Kansas,  326 

Maryland,  337,  338 

Minnesota,  348 

Mississippi,  352 

Missouri,  181,  355,  359,  360 

New  Jersey,  181 

New  York,  181,  378 

North  Carolina,  386 

Ohio,  180,  395,  397 

physical  properties,  180 

physical  tests,  181 

Texas,  181,  427,  428,  431 

uses,  182 

Stover,  E.  C.,  cited,  104 
Stream-clays,  Wisconsin,  455 
Strontium,  adsorption  by  clay,  163 
Structural  features,  sedimentary  clays,  17 
Sub-Carboniferous,  Missouri,  355 
Suffolk,  Va.,  437 

Sullivan,  adsorption  experiments  of,  164 
Sulphates,  adsorption  by  clay,  164 

in  clay,  91 
Sulphur,  in  clay,  55 

determination  of,  66 

scumming  caused  by,  157 
Sulphur  Springs,  Tex.,  428 
Summers  County,  W.  Va.,  442 
Summit  County,  Ohio,  394 
Summit  Station,  Ohio,  392 
Sunday  Creek  Valley,  Ohio,  398 
Swallows  Falls,  Md.,  335 
Swamp-clays,  30 
Sylva,  N.  C.,  385 
Sylvan  shale,  316 
Synclines,  29 
Syracuse,  N.  Y.,  376 


Table  Rock,  Neb.,  363 

Talc,  98 

Tallahassee,  Fla.,  297 

Tannin,  adsorption  by  clay,  164 

Taunton,  Mass.,  341 

Taylor,  Tex.,  428 

Taylor,  Wash.,  441 

Taylorite,  458 

Taylor-Navarro  marls,  Texas,  427 

Tennessee,  alluvial  clays,  423 

Carboniferous  clays,  421 

clays  described,  420 

Palaeozoic  clays,  421 

Pre-Cambrian  clays,  421 

references  on,  424 

referred  to,  169 

Tertiary  clays,  422 

Tensile  strength,  Beyer  and  Williams'  ex- 
periments, 127 

cause  of,  123 

definition,  120 

effect  of  mixtures  on,  127 

measurement  of,  120 


Tensile  strength,  Missouri  clays,  122 

Orton's  experiments,  123 

practical  bearing,  120 

range  in  difterent  clays,  122 

relation  to  plasticity,  120 

relation  to  texture,  123 

Ries'  experiments,  125 

stone  ware -clays,  123 

Texas  clays,  123 
Terrace-clays,  Pennsylvania,  413 

Texas,  431 

West  Virginia,  449 

See  Flood- plain  clays 
Terra- cotta,  denned,  254 

fayence,  254 

manufacture  of,  254 

referred  to,  179,  182 
Terra-cotta  clays,  described,  182 

distribution,  183 

Maryland,  337 

Missouri,  359 

Massachusetts,  340 

Nebraska,  363 

New  Jersey,  371 

properties  of,  182 

tests  of,  182,  184 

Washington,  441 
Terra-cotta  lumber,  denned,  248 
Terra-cotta  lumber  clay,  Pennsylvania,  413 
Terra  Haute,  Ind.,  313 
Tertiary  clays,  Alabama,  283 

Florida,  297 

Kentucky,  329 

Maryland,  337 

Mississippi,  352 

Missouri,  360 

New  Jersey,  370 

New  York,  378 

North  Dakota,  389 

Oklahoma,  400 

referred  to,  28,  169,  179,  185,  197,  285, 
289 

sedimentary,  17 

South  Dakota,  419 

Texas,  428 

Tennessee,  422 

Virginia,  437 

Washington,  441 

Wyoming,  457 

Tertiary,  fullers'  earth  in,  465 
Tesserse,  258 
Texas,  calcareous  clays,  56 

Carboniferous  clays,  426 

clays  described,  424 

Cretaceous  clays,  426 

lignitic  clays  in,  428 

Pleistocene,  431 

references  on,  433 

referred  to,  78,  84,  123,  165,  167,  179, 
181 

Tertiary  clays,  428 
Thermal  waters,  kaolinization  by,  6 


INDEX 


489 


Thompson,  Minn.,  348 

Thornton,  W.  Va.,  446 

Thurber,  Tex.,  426 

Tile.     See    Drain-,    Poor-,    Roofing-,    and 

Wall-tile. 
Tile  clays,  Illinois,  304 

Indiana,  307,  313 

Indian  Territory,  315 

Io,va,  316,  318 

Tennessee,  421,  422 

Wisconsin,  455 
Tioga  County,  Pa.,  407 
Tioiesti  coal,  Ohio,  393 
Tionesta  sandstone,  Ohio,  393 
Tishomingo  County,  Miss.,  352 
Titanite,  41 
Titinium,  determination  of,  66 

effect  on  clay,  84 

in  fire-clays,  176 

range  of,  fn  clays,  84 
Toil,  J.  E.,  cited,  419 
Toniwanda,  N.  Y.,  378 
Topiz,  kaolinization  of,  4,  47 
Topeka,  Kan.,  326 
Tounnaline,  in  c-lays,  41 

in  kaolin,  57,210 
Tracy  City,  Tenn.,  421 
Transported  clays,  14 
Trenton,  N.  J.,  370 

Trenton  limestone,  Missouri  clay  in,  355 
Triassic  clays,  Kansas,  327 

New  Jersey,  39,  364 

North  Carolina,  386 

Virginia,  437 
Troy,  N.  C.,  385 
Tucker  County,  W.  Va.,  442 
Tuscaloosa,  Ala.,  283 
Tuscarawas  County,  Ohio,  394,  395,  396 


U 


Uffmgton  shales,  W.  Va.,  446 
Ultimate  analysis,  explained,  59 

interpretation  of,  59 

method  of  making,  64 
Ultrimirine  clay,  199 
Union  City,  Mich.,  346 
Union  County,  Pa.,  402 
Union  Furnace,  Ohio,  394 
Unite  1  States,  residual  clays  in,  12 
Up-draft  kilns,  236 
Upper     Barren     Measures.     See  Dunkard 

series 
Upper    Coal -measures.     See    Monongahela 

series 
Upper  Cretaceous,  New  Jersey,  370 

Texas,  426,  428 
Upper  Freeport  clay,  Ohio,  397 

West  Virginia, '446 
Upper  Freeport  coal,  411 
Upper  Kittanning  clay,  Pennsylvania,  407 


Upper  Marlboro,  Md.,  337 
Upper  Mercer  coal,  Ohio,  393 
Upper  Mercer  fire-clay,  Ohio,  393,  394 
Upper  Mercer  limestone,  Ohio,  393 
Upper  Productive  Measures.     See  Monon- 
gahela aeries 
Upshur  County,  W.  Va.,  446 


Valley  Head,  Ala.,  halloysite  at,  49 
Vanadiates,  in  clay,  57 
Van  Bemmelen,  cited,  99 
Vandalia,  Mo.,  356 
Van  Hise,  C.  K.,  cited,  47 
Vanport  limestone  clay,  Ohio,  395 
Vaughan,  T.  W.,  cited,  461,  462 
Vegetation  of  clay-soil,  200 
Vermilion,  S.  Dak.,  420 
Vermont,  clays  described,  333 

references  on,  333 
Verne,  Mich.,  345 
Vintpn  County,  Ohio,  395 
Virginia,  Carboniferous  clays,  437 

clays  described,  434 

Conemaugh  series  clays,  446 

diatomaceous  earth,  437 

fullers'  earth,  462 

Pleistocene  clays,  437 

references  on,  441 

referred  to,  57,  84,  167 

residual  clays,  434 

Tertiary  clays,  437 

Triassic  clays,  437 
Vitrification,  relation  to  color,  162. 

stages  of,  138 
Vivianite,  in  clays,  58 
Vogt,  G.,  cited,  47,  104 
Vogt,  J.  H.  L.,  cited,  3,  4 
Volume,  determination  of,  132 
Volumeter  for  specific  gravity  determina- 
tion, 133 

Segers',  described,  137 
Von  Buch,  cited,  6 


W 

Waco,  Ky.,  328 
Waco,  Tex.,  427 
Wad-clay,  defined,  197 

referred  to,  272 
Walhalla,  N.  Dak.,  390 
Wallingford,  Vt,  333 
Wall-tile,  manufacture  of,  261 

referred  to,  198,  261 
Ware-clay,  defined,  196 
Washing  clay,  213 
Washington,  clays  described,  441 

references  on,  441 
Washington  County,  Ohio,  398 
Washington,  D.  C.,  296,  437 


490 


INDEX 


Wash-tubs,  manufacture  of,  276 
Water,  absorption  of,  by  clay,  86 

cneuiically  coin  Dined,  87 

effect  of,  on  clay,  86 

effect  on  black  coring,  90 

mechanically  combined,  86 

relation  to  weathering,  2 
Waupaca  County,  Wis.,  455 
Waushara  County,  Wis.,  455 
Way,  T.,  cited,  99,  163 
Weatherford,  Tex.,  426 
Weathering,  effect  on  plasticity,  104 

processes,  1 

Webb  County,  Tex.,  428 
Webster,  N.  C.,  96,  167,  385 
Wedgewood  pyrometer,  154 
Wedging-tables,  described,  266 
Weldon,  N.  C.,  385 
Wellsburg,  W.  Va.,  446 
West  Cornwall,  Conn.,  293 
West  Mills,  N.  C.,  385 
Westmoreland  County,  Pa.,  407,  411 
Weston  County,  Wyo.,  458 
West  Virginia,  Carboniferous  clays,  442 

clays  described,  442 

Devonian  clays,  442 

Dunkard  clays,  449 

Lower  Carboniferous  clays,  442 

Monongahela  series  clays,  446 

Pleistocene  clays,  449 

references  on,  451 

referred  to,  178,  179 

Silurian  clays,  442 
Wet  pan,  described,  220 

referred  to,  240,  251,  252,  257 
Wheeler,  A.  H.,  cited,  41,  49,  51,    95,  97, 
98,*  104,  121,  122,  131,  137,  138,  146, 
191,  196,  354 

classification  of,  24 
White,  I.  C.,  cited,  398,  406 
White  granite  ware,  defined,  262 
Whiteware,  decoration  of,  275 

defined,  262 

manufacture  of,  271 
White-ware  clay,  Missouri,  354.     See  also 

Kaolin 
Whitewash,  157 

prevention  of,  92 

See  Soluble  salts 
Whitney,  M.,  cited,  96 
Whitneys,  N.  J.,  371 


Williams,  I.  A.,  cited,  123,  127,  137,  192, 

251,  318 

Wilkesboro,  N.  C.,  385 
Williamsport,  Pa.,  402 
Willow  Station,  Ohio,  392 
Will's  Valley,  Ala.,  283 
Wilmington,  Tel.,  296 
Wilmont,  Va.,  437 
Windom,  N.  Y.,  376 
Wisconsin,  clays  described,  451 

minerals  in,  41 

Pleistocene  clays,  455 

references  on,  456 

referred  to,  56,  78 

residual  clay  in,  12,  452 

sedimentary  clays,  452 
Wood  County,  Wis.,  452 
Woodbine  formation,  Tex.,  427 
Woodbridge,  N.  J.,  feldspar  beds,  52 

referred  to,  196,  205,  209 
Woodbridge  fire-clay,  369 
Woodbury  County,  Iowa,  321 
Woodland,  Pa.,  406 
Woodmansie,  IST.  J.,  371 
Woodstock,  Ala.,  283 
Woods  town,  N.  J.,  83 
Woodward  County,  Okla.,  400 
Woolsey,  cited,  407 
Wrenshall,  Minn.,  351 
Wyoming,  clays  described,  457 

references  on,  458 

referred  to,  128 
Wyoming  County,  W.  Va.,  446 


Yellow  ware,  clays  for,  182, 397 
defined,  262 
manufacture  of,  270 


Zeolites,  solubility  of,  2 
Zettlitz,  Bohemia,  84,  100 

kaolin  at,  6 

Zimmer,  W.  H.,  cited,  70,  153 
Zinc-retorts,  179,  196 
Zoisite,  as  source  of  kaolinite,  47 
Zschokke,  cited,  94,  99,  103 


SHORT-TITLE     CATALOGUE 

OF  THE 

PUBLICATIONS 

OF 

JOHN   WILEY   &   SONS, 

NEW  YORK, 
LONDOK:  CHAPMAN  &  HALL,  LIMITED. 


ARRANGED  UNDER  SUBJECTS. 


Descriptive  circulars  sent  on  application.  Books  marked  with  an  asterisk  (*)  are  sold 
at  net  prices  only,  a  double  asterisk  (**)  books  sold  under  the  rules  of  the  American 
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are  bound  in  cloth  unless  otherwise  stated. 


AGRICULTURE. 

Armsby's  Manual  of  Cattle-feeding I2mo,  Si  75 

Principles  of  Animal  Nutrition.  .  .  e 8vo,    4  oo 

Budd  and  Hansen's  American  Horticultural  Manual: 

Part  I.  Propagation,  Culture,  and  Improvement i2mo, 

Part  II.  Systematic  Pomology i2mo, 

Downing's  Fruits  and  Fruit-trees  of  America 8vo, 

Elliott's  Engineering  for  Land  Drainage I2mo, 

Practical  Farm  Drainage \. i2mo, 

Graves's  Forest  Mensuration 8vo, 

Green's  Principles  of  American  Forestry i2mo, 

Grotenfelt's  Principles  of  Modern  Dairy  Practice.     (Woll.) I2mo, 

Kemp's  Landscape  Gardening I2mo, 

Maynard's  Landscape  Gardening  as  Applied  to  Home  Decoration i2mo, 

*  McKay  and  Larsen's  Principles  and  Practice  of  Butter-making 8vo: 

Sanderson's  Insects  Injurious  to  Staple  Crops I2mo, 

Insects  Injurious  to  Garden  Crops.     (In  preparation.) 
Insects  Injuring  Fruits.     (In  preparation.) 

Stockbridge's  Rocks  and  Soils 8vo,    2  50 

Winton's  Microscopy  of  Vegetable  Foods 8vo,     7  50 

Woll's  Handbook  for  Farmers  and  Dairymen i6mo,    i  50 


ARCHITECTURE. 

Baldwin's  Steam  Heating  for  Buildings I2mo,  2  50 

Bashore's  Sanitation  of  a  Country  House I2mo,  i  oo 

Berg's  Buildings  and  Structures  of  American  Railroads 4to,  5  oo 

Birkmire's  Planning  and  Construction  of  American  Theatres 8vo,  3  oo 

Architectural  Iron  and  Steel 8vo,  3  50- 

Compound  Riveted  Girders  as  Applied  in  Buildings 8vo,  2  oo 

Planning  and  Construction  of  High  Office  Buildings 8vo,  3  50 

Skeleton  Construction  in  Buildings 8vo,  3  oo 

Erigg's  Modern  American  School  Buildings 8vo,  4  oo 

I 


Carpenter's  Heating  and  Ventilating  of  Buildings 8vo,  4  oo 

Freitag's  Architectural  Engineering 8vo,  3  50 

Fireproofing  of  Steel  Buildings 8vo,         50 

French  and  Ives's  Stereotomy 8vo,         50 

Gerhard's  Guide  to  Sanitary  House-inspection ibmo,        oo 

Theatre  Fires  and  Panics I2mo,        50 

*Greene's  Structural  Mechanics 8vo,         50 

Holly's  Carpenters'  and  Joiners'  Handbook i8mo,         75 

Johnson's  Statics  by  Algebraic  and  Graphic  Methods 8vo,  2  oo 

Kidder's  Architects' and  Builders' Pocket-book.  Rewritten  Edition.  i6mo,mor.,  5  oo 

Merrill's  Stones  for  Building  and  Decoration 8vo,  5  oo 

Non-metallic  Minerals:    Their  Occurrence  and  Uses 8vo,  4  oo 

Monckton's  Stair-building 4*0,  4  oo 

Patton's  Practical  Treatise  on  Foundations 8vo,  5  oo 

Peabody's  Naval  Architecture 8vo,  7  50 

Rice's  Concrete -block  Manufacture 8vo,  2  oo 

Richey's  Handbook  for  Superintendents  of  Construction i6mo,  mor.,  4  oo 

*              Building  Mechanics'  Ready  Reference  Book.     Carpenters'  and  Wood- 
workers' Edition i6mo,  morocco,  i  50 

Sabin's  Industrial  and  Artistic  Technology  of  Paints  and  Varnish 8vo,  3  oo 

Siebert  and  Biggin's  Modern  Stone-cutting  and  Masonry 8vo,  I  50 

Snow's  Principal  Species  of  Wood 8vo,  3  50 

Sondericker's  Graphic  Statics  with  Applications  to  Trusses,  Beams,  and  Arches. 

8vo,  2  oo 

Towne's  Locks  and  Builders'  Hardware i8mo,  morocco,  3  oo 

Wait's  Engineering  and  Architectural  Jurisprudence 8vo,  6  oo 

Sheep,  6  50 

Law  of  Operations  Preliminary  to  Construction  in  Engineering  and  Archi- 
tecture  8vo,  5  oo 

Sheep,  5  50 

Law  of  Contracts 8vo,  3  oo 

Wood's  Rustless  Coatings:   Corrosion  and  Electrolysis  of  Iron  and  Steel.  .8vo,  4  oo 
Woicester  and  Atkinson's  Small  Hospitals,  Establishment  and  Maintenance, 
Suggestions  for  Hospital  Architecture,  with  Plans  for  a  Small  Hospital. 

I2mo,  i  25 

The  World's  Columbian  Exposition  of  1893 Large  4to,  i  oo 


ARMY  AND  NAVY. 

Bernadou's  Smokeless  Powder,  Nitro-cellulose,  and  the  Theory  of  the  Cellulose 

Molecule i2mo,  2  50 

*  Bruff's  Text-book  Ordnance  and  Gunnery 8vo,  6  oo 

Chase's  Screw  Propellers  and  Marine  Propulsion 8vo,  3  oo 

Cloke's  Gunner's  Examiner 8vo,  i  50 

Craig's  Azimuth 4to,  3  50 

Crehore  and  Squier's  Polarizing  Photo-chronograph 8vo,  3  oo 

*  Davis's  Elements  of  Law 8vo,  2  50 

*  Treatise  on  the  Military  Law  of  United  States 8vo,  7  oo 

Sheep,  7  50 

De  Brack's  Cavalry  Outposts  Duties.     (Carr.) 24mo,  morocco,  2  oo 

Dietz's  Soldier's  First  Aid  Handbook i6mo,  morocco,  i  25 

*  Dredge's  Modern  French  Artillery 4to,  half  morocco,  15  oo 

Durand's  Resistance  and  Propulsion  of  Ships 8vo,  5  oo 

*  Dyer's  Handbook  of  Light  Artillery i2mo,  3  oo 

Eissler's  Modern  High  Explosives 8vo,  4  oo 

*  Fiebeger's  Text-book  on  Field  Fortification Small  8vo,  2  oo 

Hamilton's  The  Gunner's  Catechism i8mo,  i  oo 

*  Hoff's  Elementary  Naval  Tactics 8vo,  i  50 

a 


Ingalls's  Handbook  of  Problems  in  Direct  Fire 8vo,  4  oo 

*  Ballistic  Tables 8vo,  i  50 

*  Lyons's  Treatise  on  Electromagnetic  Phenomena.  Vols.  I.  and  II.  .8vo,  each,  6  oo 

*  Mahan's  Permanent  Fortifications.     (Mercur.) 8vo,  half  morocco,  7  50 

Manual  for  Courts-martial i6mo,  morocco,  i  50 

*  Mercur's  Attack  of  Fortified  Places i2mo,  2  oo 

*  Elements  of  the  Art  of  War 8vo,  4  oo 

Metcalf's  Cost  of  Manufactures — And  the  Administration  of  Workshops.  .8vo,  5  oo 

*  Ordnance  and  Gunnery.     2  vols i2mo,  5  oo 

Murray's  Infantry  Drill  Regulations i8mo,  paper,  10 

Nixon's  Adjutants'  Manual 24mo,  i  oo 

Peabody's  Naval  Architecture 8vo,  7  50 

*  Phelps's  Practical  Marine  Surveying 8vo,  2  50 

Powell's  Army  Officer's  Examiner i2mo,  4  oo 

Sharpe's  Art  of  Subsisting  Armies  in  War i8mo,  morocco,  i  50 

*  Tupes  and  Poole's  Manual  of  Bayonet  Exercises  and    Musketry  Fencing. 

24010,  leather,  50 

*  Walke's  Lectures  on  Explosives 8vo,  4  oc 

Weaver's  Military  Explosives 8vo,  3  oo 

*  Wheeler's  Siege  Operations  and  Military  Mining : 8vo,  2  oo 

Winthrop's  Abridgment  of  Military  Law I2mo,  2  50 

Woodhull's  Notes  on  Military  Hygiene i6mo,  i  50 

Young's  Simple  Elements  of  Navigation i6mo,  morocco,  2  oo 


ASSAYING. 

Fletchar's  Practical  Instructions  in  Quantitative  Assaying  with  the  Blowpipe. 

I2mo,  morocco,  i  50 

Furman's  Manual  of  Practical  Assaying 8vo,  3  oo 

Lodge's  Notes  on  Assaying  and  Metallurgical  Laboratory  Experiments.  . .  .8vo,  3  oo 

Low's  Technical  Methods  of  Ore  Analysis 8vo,  3  oo 

Miller's  Manual  of  Assaying i2mo,  i  oo 

Cyanide  Process i2mo,  i  oo 

Minet's  Production  of  Aluminum  and  its  Industrial  Use.     (Waldo.) I2mo,  2  50 

O'Driscoll's  Notes  on  the  Treatment  of  Gold  Ores 8vo,  2  oo 

Ricketts  and  Miller's  Notes  on  Assaying 8vo,  3  oo 

Robine  and  Lenglen's  Cyanide  Industry.     (Le  Clerc.) 8vo,  4  oo 

Ulke's  Modern  Electrolytic  Copper  Refining. 8vo,  3  oo 

Wilson's  Cyanide  Processes i2mo,  i  50 

Chlorination  Process i2mo,  i  50 


ASTRONOMY. 

Comstock's  Field  Astronomy  for  Engineers 8vo,  2  50 

Craig's  Azimuth 4to,  3  50 

Doolittle's  Treatise  on  Practical  Astronomy 8vo,  4  oo 

Gore's  Elements  of  Geodesy 8vo,  2  50 

Hayford's  Text-book  of  Geodetic  Astronomy 8vo,  3  oo 

Merriman's  Elements  of  Precise  Surveying  and  Geodesy 8vo,  2  50 

*  Michie  and  Harlow's  Practical  Astronomy 8vo,  3  oo 

*  White's  Elements  of  Theoretical  and  Descriptive  Astronomy i2mo,  2  oo 


BOTANY. 

Davenport's  Statistical  Methods,  with  Special  Reference  to  Biological  Variation. 

i6mo,  morocco,  i  25 

Thomr  and  Bennett's  Structural  and  Physiological  Botany, i6mo,  2  25 

Westermaier's  Compendium  of  General  Botany.     (Schneider.).  , 8vo,  2  oo 


CHEMISTRY. 

Adriance's  Laboratory  Calculations  and  Specific  Gravity  Tables xamo,  i  25 

Alexeyeff's  General  Principles  of  Organic  Synthesis.     (Matthews.) 8vo,  3  oo 

Allen's  Tables  for  Iron  Analysis 8vo,  3  oo 

Arnold's  Compendium  of  Chemistry.     (Mandel.) Small  8vo.  3  50 

Austen's  Notes  for  Chemical  Students i2mo,  i  50 

Bernadou's  Smokeless  Powder. — Nitro-cellulose,  and  Theory  of  the  Cellulose 

Molecule i2mo,  2  50 

*  Browning's  Introduction  to  the  Rarer  Elements 8vo,  i  50 

Brush  and  Penfield's  Manual  of  Determinative  Mineralogy 8vo,  4  oo 

Claassen's  Beet-sugar  Manufacture.     (Hall  and  Rolfe.) 8vo,  3  oo 

Classen's  Quantitative  Chemical  Analysis  by  Electrolysis.    (Boltwcod.).  .8vo,  3  co 

Cohn's  Indicators  and  Test-papers I2mo,  2  oo 

Tests  and  Reagents 8vo,  3  oo 

Crafts's  Short  Course  in  Qualitative  Chemical  Analysis.   (Schaeffer.).  .  .i2mo,  i  50 
Dolezalek's  Theory  of  the   Lead  Accumulator   (Storage   Battery).        (Von 

Ende.) i2mo,  2  50 

Drechsel's  Chemical  Reactions.     (Merrill.) i2mo>  i  25 

Duhem's  Thermodynamics  and  Chemistry.     (Burgess.) 8vo,  4  oo 

Eissler's  Modern  High  Explosives 8vo,  4  oo 

Eff rent's  Enzymes  and  their  Applications.     (Prescott.) Svo,  3  oo 

Erdmann's  Introduction  to  Chemical  Preparations.     (Bunlap.) i2mo,  i   25 

Fletcher's  Practical  Instructions  in  Quantitative  Assaying  with  the  Blowpipe. 

i2mo,  morocco,  i  50 

Fowler's  Sewage  Works  Analyses i2mo,  2  oo 

Fresenius's  Manual  of  Qualitative  Chemical  Analysis.     (Wells.) 8vo,  5  oo 

Manual  of  Qualitative  Chemical  Analysis.  Part  I.  Descriptive.  (Wells.)  8vo,  3  oo 
System   of    Instruction    in    Quantitative    Chemical   Analysis.      (Cohn.) 

2  vols 8vo,  12  50 

Fuertes's  Water  and  Public  Health i2mo,  i  50 

Furman's  Manual  of  Practical  Assaying 8vo,  3  oo 

*  Getman's  Exercises  in  Physical  Chemistry i2mo,  2  oo 

Gill's  Gas  and  Fuel  Analysis  for  Engineers i2mo,  i  25 

Grotenfelt's  Principles  of  Modern  Dairy  Practice.     (Woll.) i2mo,  2  oo 

Groth's  Introduction  to  Chemical  Crystallography  (Marshall) i2mo,  i  25 

Hammarsten's  Text-book  of  Physiological  Chemistry.     (Mandel.) 8vo,  4  oo 

Helm's  Principles  of  Mathematical  Chemistry.     (Morgan.) i2mo,  i  50 

Bering's  Ready  Reference  Tables  (Conversion  Factors) i6mo,  morocco,  2  50 

Hind's  Inorganic  Chemistry 8vo,  3  o~ 

*  Laboratory  Manual  for  Students .  i2mo,  i  oo 

Holleman's  Text-book  of  Inorganic  Chemistry.     (Cooper.) 8vo,  2  50 

Text-book  of  Organic  Chemistry.     (Walker  and  Mott.) 8vo,  2  50 

*  Laboratory  Manual  of  Organic  Chemistry.     (Walker.) j2mo,  i  oo 

Hopkins's  Oil-chemists'  Handbook 8vo,  3  oo 

Jackson's  Directions  for  Laboratory  Work  in  Physiological  Chemistry.  .8vo,  i  25 

Keep's  Cast  Iron 8vo,  2  50 

Ladd's  Manual  of  Quantitative  Chemical  Analysis 12 mo,  i  oo 

Landauer's  Spectrum  Analysis.     (Tingle.) 8vo,  3  oo 

*  Langworthy  and  Austen.         The   Occurrence   of  Aluminium  in  Vege'able 

Products,  Animal  Products,  and  Natural  Waters 8vo,  2  oo 

Lassar-Cohn's  Practical  Urinary  Analysis.  (Lorenz.) '.  .  12010,  i  oo 

Application  of  Some  General  Reactions  to  Investigations  in  Organic 

Chemistry.  (Tingle.) I2mo,  i  oo 

Leach's  The  Inspection  and  Analysis  of  Food  with  Special  Reference  to  State 

Control 8vo,  7  50 

Lob's  Electrochemistry  of  Organic  Compounds.  (Lorenz.) 8vo,  3  oo 

Lodge's  Notes  on  Assaying  and  Metallurgical  Laboratory  Experiments.  ..  .8vo,  3  oo 

Low's  Technical  Method  of  Ore  Analysis 8vo,  3  oo 

Lunge's  Techno-chemical  Analysis.  (Cohn.) iamo  i  oo 

4 


*  McKay  and  Larsen's  Principles  and  Practice  of  Butter- making 8vo  i  50 

Mar.del's  Handbook  for  Bio-chemical  Laboratory i2mo,  i  50 

*  Martin's  Laboratory  Guide  to  Qualitative  Analysis  with  the  Blowpipe.  .  i2mo,  60 
Mason's  Water-supply.     (Considered  Principally  from  a  Sanitary  Standpoint.) 

3d  Edition,  Rewritten 8vo,  4  oo 

Examination  of  Water.     (Chemical  and  Bacteriological.) izmo,  I  25 

Matthew's  The  Textile  Fibres 8vo,  3  50 

Meyer's  Determination  of  Radicles  in  Carbon  Compounds.     (Tingle.).  .i2mo,  i  oo 

Miller's  Manual  of  Assaying I2mo,  I  oo 

Cyanide  Process i2mo,  i  oo 

Minet's  Production  of  Aluminum  and  its  Industrial  Use.     (Waldo.) ....  i2mo,  2  50 

Mixter's  Elementary  Text-book  of  Chemistry i2mo,  i  50 

Morgan's  An  Outline  of  the  Theory  of  Solutions  and  its  Results i2mo,  i  oo 

Elements  of  Physical  Chemistry i2mo,  3  oo 

*  Physical  Chemistry  for  Electrical  Engineers 12010,  i  50 

Morse's  Calculations  used  in  Cane-sugar  Factories i6mo,  morocco,  i  50 

Mulliken's  General  Method  for  the  Identification  of  Pure  Organic  Compounds. 

Vol.  I Large  8vo,  5  oo 

O'Brine's  Laboratory  Guide  in  Chemical  Analysis 8vo,  2  oo 

O'Driscoll's  Notes  on  the  Treatment  of  Gold  Ores 8vo,  2  oo 

Ostwald's  Conversations  on  Chemistry.     Part  One.     (Ramsey.) I2mo,  i  50 

"                   "               "           "             Part  Two.     (Turnbull.) i2mo,  2  oo 

*  Penfield's  Notes  on  Determinative  Mineralogy  and  Record  of  Mineral  Tests. 

8vo,  paper,  50 

Pictet's  The  Alkaloids  and  their  Chemical  Constitution.     (Biddle.) 8vo,  5  oo 

Pinner's  Introduction  to  Organic  Chemistry.     (Austen.) i2mo.  i  50 

Poole's  Calorific  Power  of  Fuels 8vo,  3  oc 

Prescott  and  Winslow's  Elements  of  Water  Bacteriology,  with  Special  Refer- 
ence to  Sanitary  Water  Analysis i2mo,  i  25 

*  Reisig's  Guide  to  Piece-dyeing 8vo,  25  oo 

Richards  and  Woodman's  Air.Water,  and  Food  from  a  Sanitary  Standpoint.  .8vo,  2  oa 
Ricketts  and  Russell's  Skeleton  Notes  upon  Inorganic  Chemistry.     (Part  I. 

Non-metallic  Elements.) 8vo,  morocco,  75 

Ricketts  and  Miller's  Notes  on  Assaying 8vo,  3  oo 

Rideal's  Sewage  and  the  Bacterial  Purification  of  Sewage 8vo,  3  50 

Disinfection  and  the  Preservation  of  Food 8vo,  4  oo 

Riggs's  Elementary  Manual  for  the  Chemical  Laboratory 8vo,  i  25 

Robine  and  Lenglen's  Cyanide  Industry.     (Le  Clerc.) 8vo,  4  oo 

Rostoski's  Serum  Diagnosis.     (Bolduan.) I2mo,  i  oo 

Ruddiman's  Incompatibilities  in  Prescriptions 8vo,  2  oc 

*  Whys  in  Pharmacy I2mo,  i  oo, 

Sabin's  Industrial  and  Artistic  Technology  of  Paints  and  Varnish 8vo,  3  oo 

Salkowski's  physiological  and  Pathological  Chemistry.     (Orndorff.) 8vo,  2  50 

Schimpf's  Text-book  of  Volumetric  Analysis. i2mo,  2  50 

Essentials  of  Volumetric  Analysis i2mo,  i  25 

*  Qualitative  Chemical  Analysis 8vo,  i  25 

Smith's  Lecture  Notes  on  Chemistry  for  Dental  Students 8vo,  2  50 

Spencer's  Handbook  for  Chemists  of  Beet-sugar  Houses i6mo,  morocco.  3  oo 

Handbook  for  Cane  Sugar  Manufacturers i6mo,  morocco,.  3  oo 

Stockbridge's  Rocks  and  Soils 8vo,  2  50 

*  Tillman's  Elementary  Lessons  in  Heat 8vo,  i  50 

*  Descriptive  General  Chemistry 8vo,  3  oo 

Treadwell's  Qualitative  Analysis.     (Hall.) 8vo,  3  oo 

Quantitative  Analysis.     (Hall.) 8vo,  4  oo 

Turneaure  and  Russell's  Public  Water-supplies 8vo,  5  oo 

Van  Deventer's  Physical  Chemistry  for  Beginners.     (Boltwood.) I2mo,  i  50 

*  Walke's  Lectures  on  Explosives 8vo,  4  oo 

Ware's  Beet-sugar  Manufacture  and  Refining .  .Small  8vo,  cloth,  4  oo 

Washington's  Manual  of  the  Chemical  Analysis  of  Rocks 8vo,  2  oo 

5 


Wassermann's  Immune  Sera :  Haemolysins,  Cytotoxins,  and  Precipitins.    (Bol- 

duan.) i2mo,  T  oo 

Weaver's  Military  Explosives 8vo,  3  oo 

Wehrenfennig's  Analysis  and  Softening  of  Boiler  Feed- Water 8vo,  A  oo 

Wells's  Laboratory  Guide  in  Qualitative  Chemical  Analysis 8vo,  i  50 

Short  Course  in  Inorganic  Qualitative  Chemical  Analysis  for  Engineering 

Students i2mo,  i  50 

Text-book  of  Chemical  Arithmetic I2mo,  i  25 

Whipple's  Microscopy  of  Drinking-water 8vo,  3  50 

Wilson's  Cyanide  Processes I2mo,  i  50 

Chlorination  Process i2mo,  i  50 

Winton's  Microscopy  of  Vegetable  Foods 8vo,  7  50 

Wulling's    Elementary    Course    in  Inorganic,  Pharmaceutical,  and  Medical 

Chemistry i2mo,  2  oo 


CIVIL  ENGINEERING. 

BRIDGES    AND    ROOFS.       HYDRAULICS.       MATERIALS    OF    ENGINEERING. 
RAILWAY  ENGINEERING. 

Baker's  Engineers'  Surveying  Instruments i2mo,  3  oo 

Bixby's  Graphical  Computing  Table Paper  19  V  -,24}  inches.  23 

**  Burr's  Ancient  and  Modern  Engineering  and  the  Isthmian  Cana ..     (Postage, 

27  cents  additional.) 8vo,  3  50 

•Comstock's  Field  Astronomy  for  Engineers 8vo,  2  50 

Davis's  Elevation  and  Stadia  Tables 8vo,  i  oo 

Elliott's  Engineering  for  Land  Drainage I2mo,  i  50 

Practical  Farm  Drainage I2mo,  i  oo 

*Fiebeger's  Treatise  on  Civil  Engineering 8vo,  5  oo 

Flemer's  Phototopographic  Methods  and  Instruments 8vo,  5  oo 

Folwell's  Sewerage.     (Designing  and  Maintenance.) 8vo,  3  oo 

Freitag's  Architectural  Engineering.     2d  Edition,  Rewritten 8vo,  3  50 

French  and  Ives's  Stereotomy 8vo,  2  50 

Goodhue's  Municipal  Improvements I2mo,  i   75 

Goodrich's  Economic  Disposal  of  Towns'  Refuse 8vo,  3  50 

Gore's  Elements  of  Geodesy , 8vo,  2  50 

Hayford's  Text-book  of  Geodetic  Astronomy 8vo,  3  oo 

Bering's  Ready  Reference  Tables  (Conversion  Factors) i6mo,  morocco,  2  50 

Howe's  Retaining  Walls  for  Earth i2iro,  i   25 

*  Ives's  Adjustments  of  the  Engineer's  Transit  and  Level i6mo,  Bds.  25 

Ives  and  Hilts's  Problems  in  Surveying i6mo,  morocco,  i  50 

Johnson's  (J.  B.)  Theory  and  Practice  of  Surveying SmaJl  8vo,  4  oo 

Johnson's  (L.  J.)  Statics  by  Algebraic  and  Graphic  Methods 8vo,  2  oo 

Laplace's  Philosophical  Essay  on  Probabilities.     (Truscott  and  Emory.) .  i2mo,  2  oo 

Mahan's  Treatise  on  Civil  Engineering.     (1873.)     (Wood.) 8vo,  5  oo 

*  Descriptive  Geometry 8vo,  i  50 

Merriman's  Elements  of  Precise  Surveying  and  Geodesy 8vo,  2  50 

Merriman  and  Brooks's  Handbook  for  Surveyors i6mo,  morocco,  2  oo 

Nugent's  Plane  Surveying 8vo,  3  50 

Ogden's  Sewer  Design , I2mo,  2  oo 

Parsons's  Disposal  of  Municipal  Refuse 8vo,  2  oo 

Patton's  Treatise  on  Civil  Engineering 8vo  half  leather,  7  50 

Reed's  Topographical  Drawing  and  Sketching 4to,  5  oo 

Rideal's  Sewage  and  the  Bacterial  Purification  of  Sewage 8vo,  3  50 

Siebert  and  Biggin's  Modern  Stone-cutting  and  Masonry 8vo,  i  50 

Smith's  Manual  of  Topographical  Drawing.     (McMillan.) 8vo,  2  50 

Sondericker's  Graphic  Statics,  with  Applications  to  Trusses,  Beams,  and  Arches. 

8vo,  2  oo 

6 


Taylor  and  Thompson's  Treatise  on  Concrete,  Plain  and  Reinforced 8vo,  5  oo 

*  Trautwine's  Civil  Engineer's  Pocket-book i6mo,  morocco,  5  oo 

Venable's  Garbage  Crematories  in  America 8vo,  2  oo 

Wait's  Engineering  and  Architectural  Jurisprudence Cvo,  6  co 

Sheep,  6  50 

Law  of  Operations  Preliminary  to  Construction  in  Engineering  and  Archi- 
tecture  8vo,  5  oo 

Sheep,  5  50 

Law  of  Contracts 8vo,  3  oo 

Warren's  Stereotomy — Problems  in  Stone-cutting 8vo,  2  50 

Webb's  Problems  in  the  Use  and  Adjustment  c2  Engineering  Instruments. 

i6mo,  morocco,  i  25 

Wilson's  Topographic  Surveying 8vo,  3  50 


BRIDGES  AND  ROOFS. 

Boiler's  Practical  Treatise  on  the  Construction  of  Iron  Highway  Bridges.  .8vo,  2  oo 

*       Thames  River  Bridge 4to,  paper,  5  oo 

Burr's  Course  on  the  Stresses  in  Bridges  and  Roof  Trusses,  Arched  Ribs,  and 

Suspension  Bridges 8vo,  3  50 

Burr  and  Falk's  Influence  Lines  for  Bridge  and  Roof  Computations 8vo,  3  o» 

Design  and  Construction  of  Metallic  Bridges 8vo.  5  oo 

Du  Bois's  Mechanics  of  Engineering.     Vol.  II Eirall  4to,  10  co 

Foster's  Treatise  on  Wooden  Trestle  Bridges 4to,  5  oo 

Fowler's  Ordinary  Foundations 8vo,  3  50 

Greene's  Roof  Trusses 8vo,  i  25 

Bridge  Trusses 8vo,  2  50 

Arches  in  Wood,  Iron,  and  Stone 8vot  2  50 

Howe's  Treatise  on  Arches 8vo,  4  oo 

Design  of  Simple  Roof- trusses  in  Wood  and  Steel 8vo,  2  oo 

Symmetrical  Masonry  Arches 8vo,  2  50 

Johnson,  Bryan,  and  Turneaure's  Theory  and  Practice  in  the  Designing  of 

Modern  Framed  Structures Small  4to,  10  oo 

Merriman  and  Jacoby's  Text-book  on  Roofs  and  Bridges: 

Part  I.     Stresses  in  Simple  Trusses 8vo,  2  50 

Part  II.    Graphic  Statics 8vo,  2  50 

Part  III.  Bridge  Design 8vo,  2  50 

Part  IV.   Higher  Structures 8vo,  2  50 

Morison's  Memphis  Bridge 4to,  10  oo 

Waddell's  De  Pontibus,  a  Pocket-book  for  Bridge  Engineers.  .  i6iro,  morocco,  2  oo 

*  Specifications  for  Steel  Bridges i2n?o,  50 

Wright's  Designing  of  Draw-spans.     Two  parts  in  one  volume 8vo,  3  50 


HYDRAULICS. 

Barnes's  Ice  Formation 8vo,  3  oo 

Bazin's  Experiments  upon  the  Contraction  of  the  Liquid  Vein  Issuing  from 

an  Orifice.     (Trautwine.) 8vo,  2  oo 

Bovey's  Treatise  on  Hydraulics 8vo,  5  oo 

Church's  Mechanics  of  Engineering .  .  .8vo,  6  oo 

Diagrams  of  Mean  Velocity  of  Water  in  Open  Channels paper,  i  50 

Hydraulic  Motors 8vo,  2  oo 

Coffin's  Graphical  Solution  of  Hydraulic  Problems i6mo,  morocco,  2  50 

Flather's  Dynamometers,  and  the  Measurement  of  Power i2mo,  3  oo 

Folwell's  Water-supply  Engineering 8vo,  4  oo 

Frizell's  Water-power 8vo,  5  oo 

7 


Fuertes's  Water  and  Public  Health .i2mo,  i  50 

Water-filtration  Works i2mo,  2  50 

Ganguillet  and  Kutter's  General  Formula  for  the  Uniform  Flow  of  Water  in 

Rivers  and  Other  Channels.     (Hering  and  Trautwine.) 8vo,  4  oo 

Hazen's  Filtration  of  Public  Water-supply 8vo,  3  oo 

Hazlehurst's  Towers  and  Tanks  for  Water- works 8vo,  2  50 

Herschel's  115  Experiments  on  the  Carrying  Capacity  of  Large,  Riveted,  Metal 

Conduits 8vo.  2  oo 

Mason's  Water-supply.     (Considered  Principally  from  a  Sanitary  Standpoint.) 

8vo,  4  oo 

Merriman's  Treatise  on  Hydraulics 8vo,  5  oo 

*  Michie's  Elements  of  Analytical  Mechanics 8vo,  4  oo 

Schuyler's   Reservoirs  for  Irrigation,   Water-power,  and   Domestic   Water- 
supply Large  8vo,  5  oo 

**  Thomas  and  Watt's  Improvement  of  Rivers      (Post.,  440.  additional. )  4to,  6  oo 

Turneaure  and  Russell's  Public  Water-supplies 8vo,  5  oo 

Wegmann's  Design  and  Construction  of  Dams 4to,  5  oo 

Water-supply  of  the  City  of  New  York  from  1658  to  1895 4to,  10  oo 

Williams  and  Hazen's  Hydraulic  Tables 8vo,  i   50 

Wilson's  Irrigation  Engineering Small  8vo,  4  oo 

Wolff's  Windmill  as  a  Prime  Mover 8vo,  3  oo 

Wood's  Turbines 8vo,  2  50 

Elements  of  Analytical  Mechanics 8vo,  3  oo 


MATERIALS  OF  ENGINEERING. 

Baker's  Treatise  on  Masonry  Construction 8vo,  5  oo 

Roads  and  Pavements 8vo,  5  oo 

Black's  United  States  Public  Works Oblong  4to,  5  oo 

*  Bovey's  Strength  of  Materials  and  Theory  of  Structures 8vo,  7  50 

Burr's  Elasticity  and  Resistance  of  the  Materials  of  Engineering 8vo,  7  50 

Byrne's  Highway  Construction 8vo,  5  oo 

Inspection  of  the  Materials  and  Workmanship  Employed  in  Construction, 

i6mo>  3  oo 

Church's  Mechanics  of  Engineering 8vo,  6  oo 

Du  Bois's  Mechanics  of  Engineering.     Vol.  I Small  4to,  7  50 

*Eckel's  Cements,  Limes,  and  Plasters 8vo,  6  oo 

Johnson's  Materials  of  Construction Large  8vo,  6  oo 

Fowler's  Ordinary  Foundations 8vo,  3  50 

Graves's  Forest  Mensuration 8vo,  4  oo 

*  Greene's  Structural  Mechanics 8vo,  2  50 

Keep's  Cast  Iron 8vo,  2  50 

Lanza's  Applied  Mechanics 8vo,  7  50 

Marten's  Handbook  on  Testing  Materials.     (Henning.)     2  vols 8vo,  7  50 

Maurer's  Technical  Mechanics 8vo,  4  oo 

Merrill's  Stones  for  Building  and  Decoration 8vo,  5  oo 

Merriman's  Mechanics  of  Materials 8vo,  5  oo 

Strength  of  Materials i2mo,  i  oo 

Metcalf'a  Steel.     A  Manual  for  Steel-users i2mo,  2  oo 

Patton's  Practical  Treatise  on  Foundations 8vo,  5  oo 

Richardson's  Modern  Asphalt  Pavements 8vo,  3  oo 

Richey's  Handbook  for  Superintendents  of  Construction i6mo,  mor.,  4  oo 

*  Ries's  Clays:  Their  Occurrence,  Properties,  and  Uses 8vo,  5  oo 

Rockwell's  Roads  and  Pavements  in  France I2mo,  i  25 

Sabin's  Industrial  and  Artistic  Technology  of  Paints  and  Varnish 8vo,  3  oo 

Smith's  Materials  of  Machines i2mo,  i  oo 

Snow's  Principal  Species  of  Wood .  8vo,  3  50 


Spalding's  Hydsaulic  Cement tamo,  2  oo 

Text-book  on  Roads  and  Pavements 121110,  2  oo 

Taylor  and  Thompson's  Treatise  on  Concrete.  Plain  and  Reinforced 8vo,  5  oo 

Thurston's  Materials  of  Engineering.     3  Parts 8vo,  8  oo 

Part  I.     Non-metallic  Materials  of  Engineering  and  Metallurgy 8vo,  2  oo 

Part  II      Iron  and  Steel 8vo,  3  50 

Part  III.     A  Treatise  on  Brasses,  Bronzes,  and  Other  Alloys  and  their 

Constituents 8vo,  2  50 

Thurston's  Text-book  of  the  Materials  of  Construction 8vo,  5  oo 

Tillson's  Street  Pavements  and  Paving  Materials 8vo,  4  oo 

Waddell's  De  Pontibus     (A  Pocket-book  for  Bridge  Engineers.)-  .i6mo,  mor.,  2  oo 

Specifications  for  Steel  Bridges i2mo,  i  25 

Wood's  (De  V.)  Treatise  on  the  Resistance  of  Materials,  and  an  Appendix  on 

the  Preservation  of  Timber 8vo,  2  oo 

Wood's  (De  V.)  Elements  of  Analytical  Mechanics 8vo,  3  oo 

Wood's  (M.  P.)  Rustless  Coatings;    Corrosion  and  Electrolysis  of  Iron  and 

Steel 8vo,  4   DO 


RAILWAY  ENGINEERING. 

Andrew's  Handbook  for  Street  Railway  Engineers 3x5  inches,  morocco,  i  25 

Berg's  Buildings  and  Structures  of  American  Railroads 4to,  5  oo 

Brook's  Handbook  of  Street  Railroad  Location i6mo,  morocco;  i  50 

Butt's  Civil  Engineer's  Field-book i6mo,  morocco,  2  50 

Crandall's  Transition  Curve i6mo,  morocco,  i  50 

Railway  and  Other  Earthwork  Tables 8vo,  i  50 

Dawson's  "Engineering"  and  Electric  Traction  Pocket-book   .  i6mo;  morccco,  5  oo 

Dredge's  History  of  the  Pennsylvania  Railroad:   (1870) Paper,  5  oo 

*  Drinker's  Tunnelling,  Explosive  Compounds,  and  Rock  Drills. 4to,  half  mor.,  25  oo 

Fisher's  Table  of  Cubic  Yards Cardboard,  25 

Godwin's  Railroad  Engineers'  Field-book  and  Explorers'  Guide.  .  .  i6mo,  mor.,  2  50 

Howard's  Transition  Curve  Field-book i6mo,  morocco,  i  50 

Hudson's  Tables  for  Calculating  the  Cubic  Contents  of  Excavations  and  Em- 
bankments  8vo,  i  oo 

Mo  liter  and  Beard's  Manual  for  Resident  Engineers.  , i6mo,  i  oo 

Nagle  s  Field  Manual  for  Railroad  Engineers i6mo,  morocco,  3  oo 

Philbrick's  Field  Manual  for  Engineers. i6mo,  morocco,  3  oo 

Searles's  Field  Engineering i6mo,  morocco,  3  oo 

Railroad  Spiral i6mo,  morocco,  i  50 

Taylor's  Prismoidal  Formulae  and  Earthwork 8vo,  i  50 

*  Trautwine's  Method  ot  Calculating  the  Cube  Contents  of  Excavations  and 

Embankments  by  the  Aid  of  Diagrams 8vo,  2  oo 

The  Field  Practice  of  Laying  Out  Circular  Curves  for  Railroads. 

I2mo,  morocco,  2  50 

Cross-section  Sheet Paper,  25 

Webb's  Railroad  Construction i6mo.  morocco,  5  oo 

Economics  of  Railroad  Construction Large  i2mo,  2  50 

Wellington's  Economic  Theory  of  the  Location  of  Railways.      ....  Small  8vo.  5  oo 


DRAWING. 

Barr's  Kinematics  of  Machinery 8vo  2  50 

*  Bartlett's  Mechanical  Drawing 8vo,  3  oo 

*  "  "  "         Abridged  Ed 8vo,  i  50 

Coolidge's  Manual  of  Drawing 8vo,  paper,  i  oo 

9 


Coolidge  and  Freeman's  Elements  of  General  Drafting  for  Mechanical  Engi- 
neers  Oblong  4to,  2  50 

Durley's  Kinematics  of  Machines 8vo,  4  oo 

Emch's  Introduction  to  Projective  Geometry  and  its  Applications 8vo,  2  50 

Hill's  Text-book  on  Shades  and  Shadows,  and  Perspective 8ro,  2  oo 

Jamison's  Elements  of  Mechanical  Drawing 8vo,  2  50 

Advanced  Mechanical  Drawing 8vo,  2  oo 

Jones's  Machine  Design: 

Part  I.     Kinematics  of  Machinery 8vo,  i  50 

Part  II.     Form,  Strength,  and  Proportions  of  Parts 8vo,  3  oo 

MacCord's  Elements  of  Descriptive  Geometry 8vo,  3  oo 

Kinematics;   or,  Practical  Mechanism. 8vo,  5  oo 

Mechanical  Drawing 4to,  4  oo 

Velocity  Diagrams 8vo,  i  50 

MacLeod's  Descriptive  Geometry Small  8vo,  i  50 

*  Mahan's  Descriptive  Geometry  and  Stone-cutting 8vo,  i  50 

Industrial  Drawing.  (Thompson.) 8vo,  3  50 

Meyer's  Descriptive  Geometry 8vo,  2  oo 

Reed's  Topographical  Drawing  and  Sketching 4to,  5  oo 

Reid's  Course  in  Mechanical  Drawing 8vo,  2  oo 

Text-book  of  Mechanical  Drawing  and  Elementary  Machine  Design.  8vo,  3  oo 

Robinson's  Principles  of  Mechanism 8vo,  3  oo 

Schwamb  and  Merrill's  Elements  of  Mechanism 8vo,  3  oo 

Smith's  (R.  S.)  Manual  of  Topographical  Drawing.  (McMillan.) 8vo,  2  50 

Smith  (A.  W.)  and  Marx's  i Tachine  Design 8vo,  3  oo 

*  Titsworth's  Elements  of  Mechanical  Drawing Oblong  8vo,  i  25 

Warren's  Elements  of  Plane  and  Solid  Free-hand  Geometrical  Drawing.  i2mo,  i  oo 

Drafting  Instruments  and  Operations i2mo,  i  25 

Manual  of  Elementary  Projection  Drawing i2mo,  i  50 

Manual  of  Elementary  Problems  in  the  Linear  Perspective  of  Form  and 

Shadow i2mo,  i  oo 

Plane  Problems  in  Elementary  Geometry i2mo,  i  25 

Primary  Geometry i2mo,  75 

Elements  of  Descriptive  Geometry,  Shadows,  and  Perspective 8vo,  3  50 

General  Problems  of  Shades  and  Shadows 8vo,  3  oo 

Elements  of  Machine  Construction  and  Drawing 8vo,  7  50 

Problems,  Theorems,  and  Examples  in  Descriptive  Geometry 8vo,  2  50 

Weisbach's    Kinematics    and    Power    of    Transmission.        (Hermann    and 

Klein.) 8vo,  5  oo 

Whelpley's  Practical  Instruction  in  the  Art  of  Letter  Engraving i2mo,  2  oo 

Wilson's  (H.  M.)  Topographic  Surveying 8vo,  3  50 

Wilson's  (V.  T.)  Free-hand  Perspective 8vo,  2  50 

Wilson's  (V.  T.)  Free-hand  Lettering 8vo,  i  oo 

Woolf's  Elementary  Course  in  Descriptive  Geometry Large  8vo,  3  OO 


ELECTRICITY  AND  PHYSICS. 

Anthony  and  Brackett's  Text-book  of  Physics.     (Magie.) .Small  8vo,  3  oo 

Anthony's  Lecture-notes  on  the  Theory  of  Electrical  Measurements.  .  .  .  i2mo,  i  oo 

Benjamin's  History  of  Electricity 8vo,  3  oo 

Voltaic  Cell 8vo,  3  oo 

Classen's  Quantitative  Chemical  Analysis  by  Electrolysis.     (Boltwood.).8vo,  3  oo 

*  Collins's  Manual  of  Wireless  Telegraphy i2mo,  i  50 

Morocco,  2  oo 

Crehore  and  Squier's  Polarizing  Photo-chronograph.  .  , 8vo,  3  oo 

Dawson's  "Engineering"  and  Electric  Traction  Pocket-book.  i6mo,  morocco,  5  oo 

10 


Dolezalek's    Theory   of    the    Lead    Accumulator    (Storage    Battery).      (Von 

Ende. ) 1 2ino,  2  50 

Duhern's  Thermodynamics  and  Chemistry.     (Burgess.) 8vo,  4  oo 

Flather's  Dynamometers,  and  the  Measurement  of  Power i2mo,  3  oo 

Gilbert's  De  Magnete.     (Mottelay.) 8vo,  2  50 

Hanchett's  Alternating  Currents  Explained I2mo,  i  oo 

Bering's  Ready  Reference  Tables  (Conversion  Factors) i6mo,  morocco,  2  50 

Holman's  Precision  of  Measurements 8vo,  2  oo 

Telescopic   Mirror-scale  Method,  Adjustments,  and   Tests.  .  .  .Large  8vo,  75 

Kinzbrunner's  Testing  of  Continuous-current  Machines 8vo,  2  oo 

Landauer's  Spectrum  Analysis.     (Tingle.) 8vo,  3  oo 

Le  Chateliers  High-temperature  Measurements.  (Boudouard — Burgess.)  i2mo,  3  oo 

Lob's  Electrochemistry  of  Organic  Compounds.     (Lorenz.) 8vo,  3  oo 

*  Lyons's  Treatise  on  Electromagnetic  Phenomena.   Vols.  I.  and  II.  8vo,  each,  6  oo 

*  Michie's  Elements  of  Wave  Motion  Relating  to  Sound  and  Light 8vo,  4  oo 

Niaudet's  Elementary  Treatise  on  Electric  Batteries.     (Fishback.) i2mo,  2  50 

*  Parshall  and  Hobart's  Electric  Machine  Design 4to,  half  morocco,  12  50 

*  Rosenberg's  Electrical  Engineering.     (Haldane  Gee — Kinzbrunner. ).  .  .8vo,  i  50 

Ryan,  Norris,  and  Hoxie's  Electrical  Machinery.     Vol.  1 8vo,  2  50 

Thurston's  Stationary  Steam-engines 8vo,  2  50 

*  Tollman's  Elementary  Lessons  in  Heat 8vo,  i  50 

Tory  and  Pitcher's  Manual  of  Laboratory  Physics Small  8vo,  2  oo 

Ulke's  Modern  Electrolytic  Copper  Refining 8vo,  3  oo 


LAW. 

*  Davis's  Elements  of  Law 8vo,  2  50 

*  Treatise  on  the  Military  Law  of  United  States 8vo,  7  oo 

*  Sheep,  7  50 

Manual  for  Courts-martial i6mo,  morocco,  i  50 

Wait's  Engineering  and  Architectural  Jurisprudence 8vo,  6  oo 

Sheep,  6  50 

Law  of  Operations  Preliminary  to  Construction  in  Engineering  and  Archi- 
tecture  8vo7  5  oo 

Sheep,  5  50 

Law  of  Contracts 8vo,  3  oo 

Winthrop's  Abridgment  of  Military  Law I2mo,  a  50 


MANUFACTURES. 

Bernadou's  Smokeless  Powder — Nitro-cellulose  and  Theory  of  the  Cellulose 

Molecule 1 21110,  2  50 

Bolland's  Iron  Founder I2mo,  2  50 

The  Iron  Founder,"  Supplement i2mo,  2  50 

Encyclopedia  of  Founding  and  Dictionary  of  Foundry  Terms  Used  in  the 

Practice  of  Moulding i2mo,  3  oo 

Claassen's  Beet-sugar  Manufacture.    (Hall  and  Rolfe.) 8vo,  3  oo 

*  Eckel's  Cements,  Limes,  and  Plasters 8vo,  6  oo 

Eissler's  Modern  High  Explosives 8vo,  4  oo 

Effront's  Enzymes  and  their  Applications.     (Prescott.) 8vo,  3  oo 

Fitzgerald's  Boston  Machinist I2mo,  i  oo 

Ford's  Boiler  Making  for  Boiler  Makers i8mo,  i  oo 

Hopkin's  Oil-chemists'  Handbook 8vo,  3  oo 

Keep's  Cast  Iron 8vo,  2  50 

11 


Leach's  The  Inspection  and  Analysis  of  Food  with  Special  Reference  to  State 

Control *. Large  8vo,  7  50 

*  McKay  and  Larsen's  Principles  and  Practice  of  Butter-making 8vo,  i  50 

Matthews's  The  Textile  Fibres 8vo,  3  So 

Metcalf's  Steel.     A  Manual  for  Steel-users i2mo,  2  oo 

Mstcalfe's  Cost  of  Manufactures — And  the  Administration  of  Workshops. 8vo,  5  oo 

Meyer's  Modern  Locomotive  Construction 4to,  10  oo 

Morse's  Calculations  used  in  Cane-sugar  Factories i6mo,  morocco,  i  50 

*  Reisig's  Guide  to  Piece-dyeing 8vo,  25  oo 

Rice's  Concrete-block  Manufacture 8vo,  2  oo 

Sabin's  Industrial  and  Artistic  Technology  of  Paints  and  Varnish 8vo,  3  oo 

Smith's  Press-working  of  Metals 8vo,  3  oo 

Spalding's  Hydraulic  Cement i2mo,  2  oo 

Spencer's  Handbook  for  Chemists  of  Beet-sugar  Houses i6mo,  morocco,  3  oo 

Handbook  for  Cane  Sugar  Manufacturers r6mo,  morocco,  3  oo 

Taylor  and  Thompson's  Treatise  on  Concrete,  Plain  and  Reinforced 8vo,  5  oo 

Thurston's  Manual  of  Steam-boilers,  their  Designs,  Construction  and  Opera- 
tion  '. 8vo,  5  oo 

*  Walke's  Lectures  on  Explosives 8vo,  4  oo 

Ware's  Beet-sugar  Manufacture  and  Refining Small  8vo,  4  oo 

Weaver's  Military  Explosives 8vo,  3  oo 

West's  American  Foundry  Practice i2mo,  2  50 

Moulder's  Text-book i2mo,  2  50 

Wolff's  Windmill  as  a  Prime  Mover 8vo,  3  oo 

Wood's  Rustless  Coatings :   Corrosion  and  Electrolysis  of  Iron  and  Steel.  .8vo,  4  oo 


MATHEMATICS. 

Baker's  Elliptic  Functions 8vo,    i  50 

*  Bass's  Elements  of  Differential  Calculus 12010,    4  oo 

Briggs's  Elements  of  Plane  Analytic  Geometry i2mo, 

Compton's  Manual  of  Logarithmic  Computations i2mo, 

Davis's  Introduction  to  the  Logic  of  Algebra 8vo, 

*  Dickson's  College  Algebra Large  i2mo, 


*  Introduction  to  the  Theory  of  Algebraic  Equations Large  i2mo, 

Emch's  Introduction  to  Projective  Geometry  and  its  Applications 8vo, 

Halsted's  Elements  of  Geometry 8vo, 

Elementary  Synthetic  Geometry 8vo, 

Rational  Geometry i2mo, 

*  Johnson's  (J.  B.)  Three-place  Logarithmic  Tables:   Vest-pocket  size. paper,        15 

100  copies  for    5  oo 

*  Mounted  on  heavy  cardboard,  8X10  inches,         25 

10  copies  for    2  oo 
Johnson's  (W  W.)  Elementary  Treatise  on  Differential  Calculus.  .Small  8vo,    3  oo 

Elementary  Treatise  on  the  Integral  Calculus Small  8vo,     i  50 

Johnson's  (W.  W.)  Curve  Tracing  in  Cartesian  Co-ordinates i2mo,     i  oo 

Johnson's  (W.  W.)  Treatise  on  Ordinary  and  Partial  Differential  Equations. 

Small  8vo,     3  50 
Johnson's  (W.  W.)  Theory  of  Errors  and  the  Method  of  Least  Squares.  i2mo,     i  50 

*  Johnson's  (W   W.)  Theoretical  Mechanics. i2mo,    3  oo 

Laplace's  Philosophical  Essay  on  Probabilities.     (Truscott  and  Emory.).  i2mos     2  oo 

*  Ludlow  and  Bass.     Elements  of  Trigonometry  and  Logarithmic  and  Other 

Tables 8vo,    3  oo 

Trigonometry  and  Tables  published  separately Each,     2  oo 

*  Ludlow's  Logarithmic  and  Trigonometric  Tables , 8vo.     i  oo 

Manning's  Irrational  Numbers  and  their  Representation  by  Sequences  and  Series 

I2mo      i  25 
12 


Mathematical  Monographs.     Edited  by  Mansfield  Merriman  and  Robert 

S.  Woodward Octavo,  each     i  oo 

No.  i.  History  of  Modern  Mathematics,  by  David  Eugene  Smith. 
No.  2.  Synthetic  Projective  Geometry,  by  George  Bruce  Halsted. 
No.  3.  Determinants,  by  Laenas  Gifford  Weld.  No.  4.  Hyper- 
bolic Funetions,  by  James  McMahon.  No.  5.  Harmonic  Func- 
tions, by  William  E.  Byerly.  No.  6.  Grassmann's  Space  Analysis, 
by  Edward  W.  Hyde.  No.  7.  Probability  and  Theory  of  Errors, 
by  Robert  S.  Woodward.  No.  8.  Vector  Analysis  and  Quaternions, 
by  Alexander  Macfarlane.  No.  9.  Differential  Equations,  by 
William  Woolsey  Johnson.  No.  10.  The  Solution  of  Equations, 
by  Mansfield  Merriman.  No.  n.  Functions  of  a  Complex  Variable, 
by  Thomas  S.  Fiskc. 

Maurer's  Technical  Mechanics.  .  „ 8vo,    4  oo 

Merrirnan's  Method  of  Least  Squares 8vo,    2  oo 

Rice  and  Johnson's  Elementary  Treatise  on  the  Differential  Calculus. .  Sm.  8vo,    3  oo 

Differential  and  Integral  Calculus.     2  vols.  in  one Small  8vo,    2  50 

Wood's  Elements  of  Co-ordinate  Geometry 8vo,    2  oo 

Trigonometry:   Analytical,  Plane,  and  Spherical .i2mo,     i  oo 


MECHANICAL  ENGINEERING. 

MATERIALS  OF  ENGINEERING,  STEAM-ENGINES  AND  BOILERS. 

Bacon's  Forge  Practice i2tno,  i  50 

Baldwin's  Steam  Heating  for  Buildings i2mo,  2  50 

Barr's  Kinematics  of  Machinery 8vo,  2  50 

*  Bartlett's  Mechanical  Drawing 8vo,  3  oo 

*  "                   "                 "        Abridged  Ed 8vo,  i  50 

Benjamin's  Wrinkles  and  Recipes i2mo,  2  oo 

Carpenter's  Experimental  Engineering 8vo,  6  oo 

Heating  and  Ventilating  Buildings 8vo,  4  oo 

Gary's  Smoke  Suppression  in  Plants  using  Bituminous  Coal.     (In  Prepara- 
tion.) 

Clerk's  Gas  and  Oil  Engine .Small  8vo,  4  oo 

Coolidge's  Manual  of  Drawing 8vo,  paper,  i  oo 

Coolidge  and  Freeman's  Elements  of  General  Drafting  for  Mechanical  En- 
gineers  Oblong  4to,  2  50 

Cromwell's  Treatise  on  Toothed  Gearing i2mo,  i  50 

Treatise  on  Belts  and  Pulleys i2mo,  i  50 

Durley's  Kinematics  of  Machines 8vo,  4  oo 

Flather's  Dynamometers  and  the  Measurement  of  Power i2mo,  3  oo 

Rope  Driving ' i2mo,  2  oo 

Gill's  Gas  and  Fuel  Analysis  for  Engineers i2mo,  i  25 

Hall's  Car  Lubrication I2mo,  i  oo 

Bering's  Ready  Reference  Tables  (Conversion  Factors) i6mo,  morocco,  2  50 

Button's  The  Gas  Engine 8vo,  5  oo 

Jamison's  Mechanical  Drawing 8vo,  2  50 

Jones's  Machine  Design: 

Part  I.     Kinematics  of  Machinery 8vo,  i  50 

Part  II.     Form,  Strength,  and  Proportions  of  Parts 8vo,  3  oo 

Kent's  Mechanical  Engineers'  Pocket-book i6mo,  morocco,  5  oo 

Kerr's  Power  and  Power  Transmission 8vo,  2  oo 

Leonard's  Machine  Shop,  Tools,  and  Methods 8vo,  4  oo 

*  Lorenz's  Modern  Refrigerating  Machinery.    (Pope,  Haven,  and  Dean.) .  . 8vo,  4  oo 
MacCord's  Kinematics;   or  Practical  Mechanism 8vo,  5  oo 

Mechanical  Drawing 4to.  4  oo 

Velocity  Diagrams.         8vo,  i  50 

13  • 


MacFar land's  Standard  Reduction  Factors  for  Gases 8vo,  i  50 

Mahan's  Industrial  Drawing.     (Thompson.), 8vo,  3  50 

Poole's  Calorific  Power  of  Fuels 8vo,  3  oo 

Reid's  Course  in  Mechanical  Drawing 8vo,  2  oo 

Text-book  of  Mechanical  Drawing  and  Elementary  Machine  Design. 8vo,  3  oo 

Richard's  Compressed  Air lamo,  i  50 

Robinson's  Principles  of  Mechanism 8vo,  3  oo 

Schwamb  and  Merrill's  Elements  of  Mechanism 8vo,  3  oo 

Smith's  (O.)  Press-working  of  Metals 8vo,  3  oo 

Smith  (A.  W.)  and  Marx's  Machine  Design 8vo,  3  oo 

Thurston's   Treatise   on   Friction  and   Lost   Work   in   Machinery   and   Mill 

Work..  . , 8vo,  3  oo 

Animal  as  a  Machine  and  Prime  Motor,  and  the  Laws  of  Energetics.  1 2mo,  i  oo 

Warren's  Elements  of  Machine  Construction  and  Drawing 8vo,  7  5^ 

Weisbach's    Kinematics    and    the    Power    of    Transmission.     (Herrmann — 

Klein.). 8vo,  5  oo 

Machinery  of  Transmission  and  Governors.     (Herrmann — Klein.).  .8vo,  500 

Wolff's  Windmill  as  a  Prime  Mover 8vo,  3  oo 

Wood's  Turbines 8vo,  2  50 


MATERIALS   OP  ENGINEERING. 

*  Bovey's  Strength  of  Materials  and  Theory  of  Structures 8vo,  7  50 

Burr's  Elasticity  and  Resistance  of  the  Materials  of  Engineering.     6th  Edition. 

Reset 8vo,  7  50 

Church's  Mechanics  of  Engineering 8vo,  6  oo 

*  Greene's  Structural  Mechanics 8vo,  2  50 

Johnson's  Materials  of  Construction 8vo,  6  oo 

Keep's  Cast  Iron . 8vo,  2  50 

Lanza's  Applied  Mechanics 8vo,  7  50 

Martens's  Handbook  on  Testing  Materials.     (Henning.) 8vo,  7  50 

Maurer's  Technical  Mechanics 8vo,  4  oo 

Merriman's  Mechanics  of  Materials 8vo,  5  oo 

Strength  of  Material.. i2mo,  i  oo 

Metcalf's  Steel.     A  man^a^  Icr  Steel-users i2mo,  2  oo 

Sabin's  Industrial  and  Artistic  Technology  of  Paints  and  Varnish 8vo,  3  oo 

Smith's  Materials  of  Machines i2mo,  i  oo 

Thurston's  Materials  of  Engineering 3  vols.,  8vo,  8  oo 

Part  II.     Iron  and  Steel 8vo,  3  50 

Part  III.     A  Treatise  on  Brasses,  Bronzes,  and  Other  Alloys  and  their 

Constituents 8vo,  2  50 

Text-book  of  the  Materials  of  Construction 8vo,  5  oo 

Wood's  (De  V.)  Treatise  on  the  Resistance  of  Materials  and  an  Appendix  on 

the  Preservation  of  Timber 8vo,  2  oo 

Elements  of  Analytical  Mechanics 8vo,  3  oo 

Wood's  (M.  P  )  Rustless  Coatings:    Corrosion  and  Electrolysis  of  Iron  and 

Steel 8vo,  4  oo 


STEAM-ENGINES  AND  BOILERS. 

Berry's  Temperature-entropy  Diagram I2mo,  i  25 

Carnot's  Reflections  on  the  Motive  Power  of  Heat.     (Thurston.),     .     .  .i2mo,  I  50 

Dawson's  "Engineering"  and  Electric  Traction  Pocket-book.  .  .  .i6mo  mor.,  5  oo 

Ford's  Boiler  Making  for  Boiler  Makers i8mo,  i  oo 

Goss's  Locomotive  Sparks 8vo,  2  oo 

Hemenway's  Indicator  Practice  and  Steam-engine  Economy 12010,  2  oo 

14 


Button's  Mechanical  Engineering  of  Power  Plants 8vo,  5  oo 

Heat  and  Heat-engines 8vo  5  oo 

Kent's  Steam  boiler  Economy 8vo,  4  oo 

Kneass's  Practice  and  Theory  of  the  Injector 8vo,  i   50 

MacCord's  Slide-valves 8vo,  2  oo 

Meyer's  Modern  Locomotive  Construction 4to,  10  oo 

Peabody's  Manual  of  the  Steam-engine  Indicator f2mo,  I  50 

Tables  of  the  Properties  of  Saturated  Steam  and  Other  Vapors    8vo,  i  oo 

Thermodynamics  of  the  Steam-engine  and  Other  Heat-engines 8vo,  5  oo 

Valve-gears  for  Steam-engines 8vo,  2  50 

Peabody  and  Miller's  Steam-boilers 8vo,  4  oo 

Pray's  Twenty  Years  with  the  Indicator Large  8vo,  2  50 

Pupin's  Thermodynamics  of  Reversible  Cycles  in  Gases  and  Saturated  Vapors. 

(Osterberg.) i2ino,  i  25 

Reagan's  Locomotives :   Simple   Compound,  and  Electric i2mo,  2  50 

Rontgen's  Principles  of  Thermodynamics.     (Du  Bois.) 8vo,  5  o® 

Sinclair's  Locomotive  Engine  Running  and  Management i2mo,  2  oo 

Smart's  Handbook  of  Engineering  Laboratory  Practice i2mo,  2  50 

Snow's  Steam-boiler  Practice. 8vo,  3  oo 

Spangler's  Valve-gears 8vo,  2  30 

Notes  on  Thermodynamics , i2mo,  i  oo 

Spangler,  Greene,  and  Marshall's  Elements  of  Steam-engineering 8vo,  3  oo 

Thomas's  Steam-turbines 8vo,  3  50 

Thurston's  Handy  Tables 8vo,  i  50 

Manual  of  the  Steam-engine 2  vols.,  8vo,  10  oo 

Part  I.     History,  Structure,  and  Theory 8vo,  6  oo 

Part  II.     Design,  Construction,  and  Operation 8vo,  6  oo 

Handbook  of  Engine  and  Boiler  Trials,  and  the  Use  of  the  Indicator  and 

the  Prony  Brake 8vo,  5  oo 

Stationary  Steam-engines 8vo,  2  50 

Steam-boiler  Explosions  in  Theory  and  in  Practice i2mo,  i  50 

Manual  of  Steam-boilers,  their  Designs,  Construction,  and  Operation 8vo,  5  oo 

Wehrenfenning's  Analysis  and  Softening  of  Boiler  Feed-water  (Patterson)  8vo,  4  oo 

Weisbach's  Heat,  Steam,  and  Steam-engines.     (Du  Bois.) 8vo,  5  oo 

Whitham's  Steam-engine  Design 8vo,  5  oo 

Wood's  Thermodynamics,  Heat  Motors,  and  Refrigerating  Machines.  .  .8vo,  4  o<> 


MECHANICS  AND  MACHINERY. 

Barr's  Kinematics  of  Machinery 8vo,  2  50 

*  Bovey's  Strength  of  Materials  and  Theory  of  Structures   8vo,  7  50 

Chase's  The  Art  'of  Pattern-making i2mo,  2  50 

Church's  Mechanics  of  Engineering 8vo,  6  oo 

Notes  and  Examples  in  Mechanics 8vo,  oo 

Compton's  First  Lessons  in  Metal-working I2mo,  50 

Compton  and  De  Groodt's  The  Speed  Lathe i2mo,  50 

Cromwell's  Treatise  on  Toothed  Gearing 12010,  50 

Treatise  on  Belts  and  Pulleys i2mo,  50 

Dana's  Text-book  of  Elementary  Mechanics  for  Colleges  and  Schools.  .  i2mo,  50 

Dingey's  Machinery  Pattern  Making i2mo,  oo 

Dredge's  Record  of  the   Transportation  Exhibits  Building  of  the   World's 

Columbian  Exposition  of  1893 4to  half  morocco,  5  oo 

u  Bois's  Elementary  Principles  of  Mechanics: 

Vol.      I.     Kinematics . 8vo,  3  50 

Vol.    II.     Statics 8vo,  4  oo 

Mechanics  of  Engineering.     Vol.    I Small  4to,  7  50 

VoL  II. Small  4to,  10  oo 

Durley's  Kinematics  of  Machines.      8vo,  4  oo 

15 


Fitzgerald's  Boston  Machinist i6mo,  i  oo 

Flather's  Dynamometers,  and  the  Measurement  of  Power i2mo,  3  oo 

Rope  Driving i2mo,  2  oo 

Goss's  Locomotive  Sparks 8vo,  2  oo 

*  Greene's  Structural  Mechanics 8vo,  2  50 

Hall's  Car  Lubrication i2mo,  i  oo 

Holly's  Art  of  Saw  Filing i8mo,  75 

James's  Kinematics  of  a  Point  and  the  Rational  Mechanics  of  a  Particle. 

Sma'.l  8vo,  2  oo 

*  Johnson's  (W.  W.)  Theoretical  Mechanics i2mo,  3  o<t 

Johnson's  (L.  J.)  Statics  by  Graphic  and  Algebraic  Methods »  .  .  .8vo,  2  oo 

Jones's  Machine  Design: 

Part    I.     Kinematics  of  Machinery 8vo,  i   50 

Part  H.     Form,  Strength,  and  Proportions  of  Parts.    8vo,  3  oo 

Kerr's  Power  and  Power  Transmission 8vo,  2  oo 

Lanza's  Applied  Mechanics * 8vo,  7  50 

Leonard's  Machine  Shop,  Tools,  and  Methods 8vo,  4  oo 

*  Lorenz's  Modern  Refrigerating  Machinery.     (Pope,  Haven,  and  Dean.). 8vo,  4  oo 
MacCord's  Kinematics;  or.  Practical  Mechanism 8vo,  5  oo 

Velocity  Diagrams 8vo,  i  50 

*  Martin's  Text  Book  on  Mechanics,  Vol.  I,  Statics i2mo,  i  25 

Maurer's  Technical  Mechanics 8vo,  4  oo 

Merriman's  Mechanics  of  Materials 8vo,  5  oo 

*  Elements  of  Mechanics .' i2mo,  i  oo 

*  Michie's  Elements  of  Analytical  Mechanics 8vo,  4  oo 

*  Parshalland  Hobart's  Electric  Machine  Design 4to,  half  morocco,  12  50 

Reagan's  Locomotives     Simple,  Compound,  and  Electric i2mo,  2  50 

Reid's  Course  in  Mechanical  Drawing 8vo,  2  oo 

Text-book  of  Mechanical  Drawing  and  Elementary  Machine  Design. 8vo,  3  oo 

Richards's  Compressed  Air i2mo,  i  50 

Robinson's  Principles  of  Mechanism 8vo,  3  oo 

Ryan,  Norris,  and  Hoxie's  Electrical  Machinery.     Vol.  1 8vo,  2  50 

Sanborn's  Mechanics:  Problems Large  i2mo,  i   50 

Schwamb  and  Merrill's  Elements  of  Mechanism. 8vo,  3  oo 

Sinclair's  Locomotive-engine  Running  and  Management i2mo,  2  oo 

Smith's  (O.)  Press-working  of  Metals 8vo,  3  oo 

Smith's  (A.  W.)  Materials  of  Machines i2mo,  i  oo 

Smith  (A.  W.)  and  Marx's  Machine  Design 8vo,  3  oo 

Spangbr,  Greene,  and  Marshall's  Elements  of  Steam-engineering 8vo,  3  oo 

Thurston's  Treatise  on  Friction  and  Lost  Work  in    Machinery  and    Mill 

Work 8vo,  3  oo 

Animal  as  a  Machine  and  Prime  Motor,  and  the  Laws  of  Energetics.  i2mo,  i  oo 

Warren's  Elements  of  Machine  Construction  and  Drawing 8vo,  7  50 

Weisbach's  Kinematics  and  Power  of  Transmission.   (Herrmann — Klein.).  8vo,  5  oo 

Machinery  of  Transmission  and  Governors.      (Herrmann — K?ein.).8vo,  5  oo 

Wood's  Elements  of  Analytical  Mechanics 8vo,  3  oo 

Piinciples  of  Elementary  Mechanics I2mo,  i  25 

Turbines 8vo,  2  50 

The  World's  Columbian  Exposition  of  1893 4to,  i  oo 


METALLURGY. 

Egleston's  Metallurgy  of  Silver,  Gold,  and  Mercury 

Vol.    I.     Silver 8vo,  7  50 

Vol.  II.     Gold  and  Mercury. .    8vo,  7  50 

Goesel's  Minerals  and  Metals:     A  Reference  Book ; .  .  .  .  i6mo,  mor.  3  oo 

**  Iles's  Lead-smelting.     (Postage  9  cents  additional.) I2mo,  2  50 

Keep's  Cast  Iron 8vo,  2  50 

16 


Kunhardt's  Practice  of  Ore  Dressing  in  Europe.  « 8vo,  i  50 

Le  Chatelier's  High-temperature  Measurements.  (Boudouard — Burgess.  )i2mo.  3  oo 

Metcalf' s  Steel.     A  Manual  for  Steel-users 12010,  2  oo 

Miller's  Cyanide  Process i2mo,  i  oo 

Minet's  Production  of  Aluminum  and  its  Industrial  Use.     (Waldo.). ..  .  i2mo,  2  50 

Robine  and  Lenglen's  Cyanide  Industry.     (Le  Clerc.) 8vo,  4  oo 

Smith's  Materials  of  Machines I2mo,  i  oo 

Thurston's  Materials  of  Engineering.     In  Three  Parts 8vo,  8  oo 

*  Part    II.     Iron  and  Steel 8vo,  3  50 

Part  III.     A  Treatise  on  Brasses,  Bronzes,  and  Other  Alloys  and  their 

Constituents 8vo,  2  50 

Ulke's  Modern  Electrolytic  Copper  Refining 8vo,  3  oo 


MINERALOGY. 

Barringer's  Description  of  Minerals  of  Commercial  Value.    Oblong,  morocco,  2  50 

Boyd's  Resources  of  Southwest  Virginia 8vo,  3  oo 

Map  of  Southwest  Virignia Pocket-book  form.  2  oo 

Brush's  Manual  of  Determinative  Mineralogy.     (Penfield.) .Svo,  4  oo 

Chester's  Catalogue  of  Minerals 8vo,  paper,  i  oo 

Cloth,  i   25 

Dictionary  of  the  Names  of  Minerals 8vo  3  50 

Dana's  System  of  Mineralogy Large  8vo,  half  leather    12  50 

First  Appendix  to  Dana's  New  "  System  of  Mineralogy." Large  8vo,  i  oo 

Text-book  of  Mineralogy 8vo,  4  oo 

Minerals  and  How  to  Study  Them I2mo,  i  50 

Catalogue  of  American  Localities  of  Minerals Large  8vo,  i  oo 

Manual  of  Mineralogy  and  Petrography 12010,  2  oo 

Douglas's  Untechnical  Addresses  on  Technical  Subjects i2mo,  i  oo 

Eakle's  Mineral  Tables 8vo,  i  25 

Egleston's  Catalogue  of  Minerals  and  Synonyms 8vo,  2  50 

Goesel's  Minerals  and  Metals :     A  Reference  Book i6mo,mor..  3  oo 

Groth's  Introduction  to  Chemical  Crystallography  (Marshall) i2mo,  i  25 

Hussak's  The  Determination  of  Rock-forming  Minerals.    ( Smith.). Small  8vo,  2  oo 

Merrill's  Non-metallic  Minerals-   Their  Occurrence  and  Uses Svo,  4  oo 

*  Penfield's  Notes  on  Determinative  Mineralogy  and  Record  of  Mineral  Tests. 

Svo,  paper,  50 
Rosenbusch's   Microscopical  Physiography   of   the   Rock-making  Minerals. 

(Iddings.) Svo,  5  oo 

*  Tillman's  Text-book  of  Important  Minerals  and  Rocks Svo,  2  oo 


MINING. 

Beard's  Ventilation  of  Mines I2mo,  2  50 

Boyd's  Resources  of  Southwest  Virginia 8vos  3  oo 

Map  of  Southwest  Virginia. , Pocket-book  form  2  oo 

Douglas's  Untechnical  Addresses  on  Technical  Subjects i2mo,  i  oo 

*  Drinker's  Tunneling,  Explosive  Compounds,  and  Rock  Drills.  .4to,lif.  mor.>  25  oo 

Eissler's  Modern  High  Explosives 8n  4     r 

Goesel's  Minerals  and  Metals  •     A  Reference  Book .  .      i6mo,  mor.  3  oo 

Goodyear's  Coal-mines  of  the  Western  Coast  of  the  United  States i2mo,  2  50 

Ihlseng's  Manual  of  Mining Svo,  5  oo 

**  Iles's  Lead-smelting.     (Postage  QC.  additional.) i2mo,  2  50 

Kunhardt's  Practice  of  Ore  Dressing  in  Europe.  .  .    Svo,  i  50 

Miller's  Cyanide  Process i2mo,  i  oo 

17 


O'Driscoll's  Notes  on  the  Treatment  of  Gold  Ores 8vo,  2  oo 

Robine  and  Lenglen's  Cyanide  Industry.     (Le  Clerc.) 8vo,  4  oo 

*  Walke's  Lectures  on  Explosives 8vo,  4  oo 

Weaver's  Military  Explosives 8vo,  3  oo 

Wilson's  Cyanide  Processes : I2mo,  i  50 

Chlorination  Process lamo,  i  50 

Hydraulic  and  Placer  Mining i2mo,  2  oo 

Treatise  on  Practical  and  Theoretical  Mine  Ventilation T2mo,  125 


SANITARY  SCIENCE. 

Bashore's  Sanitation  of  a  Country  House i2mo,  i  oo 

*  Outlines  of  Practical  Sanitation i2mo,  i   25 

Folwell's  Sewerage.     (Designing,  Construction,  and  Maintenance.) 8vo,  3  oo 

Water-supply  Engineering 8vo,  4  oc 

Fowler's  Sewage  Works  Analyses i2mo,  2  oo 

Fuertes's  Water  and  Public  Health i2mo,  i  50 

Water-filtration  Works i2mo,  2  50 

Gerhard's  Guide  to  Sanitary  House-inspection i6mo,  i  oo 

Goodrich's  Economic  Disposal  of  Town's  Refuse Demy  8vo,  3  50 

Hazen's  Filtration  of  Public  Water-supplies 8vo,  3  oo 

Leach's  The  Inspection  and  Analysis  of  Food  with  Special  Reference  to  State 

Control 8vo,  7  50 

Mason's  Water-supply.  (Considered  principally  from  a  Sanitary  Standpoint)  8vo,  4  oo 

Examination  of  Water.     (Chemical  and  Bacteriological.) I2mo,  i  25 

Ogden's  Sewer  Design i2mo,  2  oo 

Prescott  and  Winslow's  Elements  of  Water  Bacteriology,  with  Special  Refer- 
ence to  Sanitary  Water  Analysis i2mo,  i  25 

*  Price's  Handbook  on  Sanitation I2mo,  i  50 

Richards's  Cost  of  Food.     A  Study  in  Dietaries i2mo,  i  oo 

CosUof  Living  as  Modified  by  Sanitary  Science i2mo,  i  oc 

Cost  of  Shelter 12010,  i  oo 

Richards  and  Woodman's  Air,  Water,  and  Food  from  a  Sanitary  Stand- 
point  8vo,  2  oo 

*  Richards  and  Wiiliams's  The  Dietary  Computer 8vo,  i  50 

Rideal's  Sewage  and  Bacterial  Purification  of  Sewage 8vo,  3  50 

Turneaure  and  Russell's  Public  Water-supplies 8vo,  5  oo 

Von  Behring's  Suppression  of  Tuberculosis.     (Bolduan.) I2mo,  i  oo 

Whipple's  Microscopy  of  Drinking-waten 8vo,  3  50 

Winton's  Microscopy  of  Vegetable  Foods 8vo,  7  50 

Woodhull's  Notes  on  Military  Hygiene i6mo,  i   50 

*  Personal  Hygiene i2mo,  i  oo 


MISCELLANEOUS. 

De  Fursac's  Manual  of  Psychiatry.     (Rosanoff  and  Collins.).  .  .  .Large  i2mo,  2  50 

Ehrlich's  Collected  Studies  on  Immunity  (Bolduan) 8vo,  C  oo 

Emmons's  Geological  Guide-book  of  the  Rocky  Mountain  Excursion  of  the 

International  Congress  of  Geologists Large  £vo,  i  50 

Ferrel's  Popular  Treatise  on  the  Winds 8vo-  4  oo 

Haines's  American  Railway  Management i2mo,  2  50 

Mott's  Fallacy  of  the  Present  Theory  of  Sound i6mo,  i  oo 

Ricketts's  History  of  Rensselaer  Polytechnic  Institute,  1824-1894.. Small  8vo,  3  oo 

Rostoski's  Serum  Diagnosis.     (Bolduan.) 1 2mo  i  oo 

Rotherham's  Emphasized  New  Testament r Large  Svo,  3  oo 

18 


Steel's  Treatise  on  the  Diseases  of  the  Dog 8vo,  3  50 

The  World's  Columbian  Exposition  of  1893 4to,  i  oo 

Von  Behring's  Suppression  of  Tuberculosis.     (Bolduan.) i2mo,  i  oo 

Winslow's  Elements  of  Applied  Microscopy i2mo,  i  50 

Worcester  and  Atkinson.     Small  Hospitals,  Establishment  and  Maintenance; 

Suggestions  for  Hospital  Architecture :  Plans  for  Small  Hospital .  1 2mo ,  125 


HEBREW  AND  CHALDEE  TEXT-BOOKS. 


Green's  Elementary  Hebrew  Grammar izmo,  i  25 

Hebrew  Chrestomathy 8vo,  2  oo 

Gesenius's  Hebrew  and  Chaldee  Lexicon  to  the  Old  Testament  Scriptures. 

(Tregelles.) . .  .Small  4to,  half  morocco,  5  oo 

Letteris's  Hebrew  Bible 8vo,  2  25 

19 


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APR 


£D  2l-< 


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U.C.  BERKELEY  LIBRARIES 


155021 


